D-YAML: Sync with v0.9.2 release

Dub: Introduce a class to use in unittests ...

Currently, unit tests for dub fails on my machine
as I have a custom registry configured. This is a great
example as to why unittests shouldn't do IO or depend on the
environment, as they can randomly fail. The new TestDub class,
private to dub-application at the moment, is a band-aid for this.
I am hoping that over time, we can perform more dependency injection
with the same method as used here (or by providing a class that encloses
all IO) so that we do not need to subclass Dub.

Windows: Don't copy import .lib & .exp files for executables ...

One aspect of issue #2377 - copy those for DLLs only.

Remove redundant null checks in DependencyVersionResolver ...

We're never passing null because if we were, a SEGV would happen earlier.
But just in case, add a few asserts.

add $DPATH environment variable for file locations (#2281) ...

* error out on unknown environment variables

* add env + config for package + settings locations

fix #229

* adjust to review, extend $DPATH test

* review round 2

Merge pull request #2424 from WebFreak001/avoid-extra-mainfile-scan ...

only do main file searching when neccessary

Signed-off-by: Nicholas Wilson <thewilsonator@users.noreply.github.com>
Merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

PackageManager: Deprecate overloads of getPackage with string version

reduce FS access count for main file generation ...

as all the sourcePaths are checked and the last one is used, we just go
through all the sourcePaths in reverse and break when the first one is
found.

only do main file searching when neccessary

Trivial: Expand body of Dependency.opEquals ...

While the m_value difference is the common case,
the other ones need to be checked as well,
so put them first as they are cheaper.
Additionally, having three expressions on a single
return is not ideal for coverage / break,
so split it into 3 lines.

Dependency: Make VersionRange.match scope

Dub: Move environment read one level up the stack ...

Avoid a unittest modifying the environment,
and pave the way for having a single read of this variable,
instead of once per function call.

Deprecate Dub.getPackageSuppliers ...

As it really should be an implementation details (only called from the ctors),
and the name is misleading as it reads the environment and the config.

Dub: Remove unused m_overrideSearchPaths member ...

It was likely moved in the PackageManager ages ago.

Configy: Integrate a fix around circular reference ...

Because NestedFieldRef references the parent's (FR) Name/FieldName,
it causes a circular reference error with parseAs.

Avoid calls to .dup in cmake.d (#2421)

Trivial: Group 'Dub' class ctor/init together

Forward flag `--color={on,off}` to compiler calls (#2382) ...

When the user sets the color mode explicitly,
we forward it to the compiler for consistency,
while making sure it doesn't impact the build cache ID.

Dependency: Take advantage of -preview=in ...

Since -preview=in is now used by dub for Configy,
we might as well take advantage of it here too.

Fix #2348 Crash when describing postBuildCommands

Add changelog entry for colored output

LDC: Use `-fvisibility=public -dllimport=all` when compiling a Windows DLL (#2412) ...

As `-shared` can only be used when linking the DLL in the same cmdline too.
On Windows, `-shared` changes the defaults of some important settings wrt.
dllim/export, so specify those explicitly when *compiling* a DLL with dub
(or some static lib dependency thereof etc.).

Recursively link all link deps of dynamic libraries too (#2414) ...

Templates exposed by a dynamic library A can easily lead to
instantiations in dependees needing to be linked against a direct or
indirect dependency of A.

Trivial: Add attributes and documentation to PackageRecipe ...

While the attributes aren't used yet, they are self-descriptive,
and they improve code readability.

Trivial: Make more obvious to developers how to debug YAML parsing ...

This might not be obvious to developers, and the name might not
stick, so just add a comment for future users.

git ignore files generated by scripts/ci/travis.sh and move ignores from .gitignore to test/.gitignore

Configy: Replace parseField with parseAs ...

This removes the need to keep the representation around and have
it stored in a field of the enclosing struct.

Rename CLI flag --colors to --color any D code symbols accordingly

Configy: Synchronize with upstream ...

Bring in changes up to commit 45d8855.

Use SHA256 in place of MD5 in computeBuildName