Move most CI scripts in scripts/ci ...

The root directory was getting a bit crowded.
semaphore-ci.sh was not moved, because there's no visible way to configure semaphore from the repository.
Additionally, build.d is left in the root directory as it's useful to have it here,
and it'll be only one script one build.sh, build.cmd, and build-gdc.sh are gone.

Remove unused Jenkinsfile

Update LDC/DMD to the latest version

Remove activation of the compiler in travis-ci.sh ...

It is not necessary when run from Travis, as the compiler is already activated.
When run from semaphore-ci, just source it on install.
It also allows removing a custom step in dlang/ci's config.

Merge pull request #1844 from Geod24/searchpath ...

Clean up PackageManager handling of search path
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Merge pull request #1851 from MartinNowak/merge_stable ...

Merge remote-tracking branch 'upstream/stable' into merge_stable
merged-on-behalf-of: Mathias LANG <pro.mathias.lang@gmail.com>

Merge remote-tracking branch 'upstream/stable' into merge_stable

update version to v1.19.0

Merge pull request #1849 from Geod24/more-script-replacements ...

Use build.d everywhere, fix windows build
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Fix Windows binary releases

Add zsh completion script ...

Currently supports the main dub commands: build, init, run, test, clean, dustmite...
Reads the local packages from dub whenever possible.
A few improvements to dub will be necessary to make it completely useful (e.g. display configurations).

Use build.d everywhere and take arguments by parameter ...

It seems easier to forward arguments from the build script this way,
and it's much more common to change the build arguments than the version.

Merge pull request #1848 from Geod24/fix1474 ...

Add a warning / workaround for issue 1474
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Fix issue 1277: Missing dub.json causes infinite loop ...

For some reason, having a 'source/app.d' was recognized as being in a package.
This would load an empty package with no manifest and send the dependency resolver
in an infinite loop.
Remove the special detection of 'source/app.d' and rely only on manifest.
Another option would have been to detect 'source/app.d' as a single-file package,
but that is a bit too much magic (the user can just 'dub run --single source/app.d').

Add a warning / workaround for issue 1474

example/generated-sources: Quote shell arguments

Merge pull request #1833 from Geod24/scripts-replacement ...

Improve travis-ci.sh
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Merge pull request #1843 from MartinNowak/merge_stable ...

Merge remote-tracking branch 'upstream/stable' into merge_stable
merged-on-behalf-of: Mathias LANG <pro.mathias.lang@gmail.com>

Deprecate compatibility overload in PackageManager

Clean up PackageManager handling of search path ...

The PackageManager is a complicated beast:
it is responsible for handling the local caches where downloaded
packages are stored, including looking up a specific version of a specific package.

One feature that stood out while going over the code was the ability to disable
the default search path.
After looking up inside of Dub more, it turns out that this feature is exclusively
used when dub is called with the '--bare' option.

However, when this happen, a special constructor of the Dub class is called,
one that calls the 'PackageManager' constructor with 3 dummy arguments,
and rely on a boolean being set to avoid those 3 dummy arguments having any effect.
This ends up with effectively providing the ability to toggle the ability to
search default search paths in theory, but in practice the dummy arguments
means that it wouldn't work, nor is it actually needed.

Instead, a special argument for the single-search path approach is provided now.
In order not to break library users, the public symbols have been deprecated,
but their usage still works.
Note that some symbols are deeply entangled: for example, 'Dub.m_overrideSearchPath'
being non-empty means that 'PackageManager.m_disableDefaultSearchPaths' is 'true'.
It also means that 'PackageManager.m_repositories' is unused (and can be empty).
Hopefully removing the ability to toggle the default search path will allow
us to simplify things and make 'PackageManager.m_repositories' the only way
to specify whether or not the default packages search path are used.

Note that additionally to the changes aiming to deprecate 'Dub.m_overrideSearchPath'
and 'PackageManager.m_disableDefaultSearchPath', an unused constructor of PackageManager
has been deprecated.

Merge pull request #1821 from Geod24/build-script ...

Replace `build.sh` and `build.cmd` with `build.d`
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Merge remote-tracking branch 'upstream/stable' into merge_stable

Merge pull request #1842 from Geod24/changelog ...

Remove leftover and outdated CHANGELOG.md file

Merge pull request #1838 from Geod24/cleanup ...

Windows: Remove Roaming repository migration
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

update version to v1.19.0-rc.1

Remove traces of VibeCustomMain ...

VibeCustomMain support was removed in Vibe.d v0.7.0,
released over 4 years ago (2015-11-04).

Remove leftover and outdated CHANGELOG.md file ...

DUB switched to using fragments from the 'changelog' directory
in PR1455 (v1.10, 2018-07-04), but the CHANGELOG.md was left
in place with the assumption a script to maintain it would
be written.
However, no such script has been written, and there doesn't
need to be a need for one either.

Merge pull request #1841 from ShigekiKarita/fix-stdout-flush ...

add flush before reading input for Windows msys2/mingw
merged-on-behalf-of: Petar Kirov <PetarKirov@users.noreply.github.com>

remove version (Windows)

add flush before reading input