Set default compiler to be the same that built dub

Add a --missing-only switch to "dub upgrade". Fixes #271.

Use URL and Path types of vibe.d if available for better interop.

Rename UpdateOptions->UpgradeOptions and move it to dub.dub.

Avoid exponential run time in the dependency resolution algorithm if possible. ...

When going through all combinations of package versions, all sub trees of the search space are now skipped for a conflicting node, as those are guaranteed to conflict anyway.

Disable log output during "dub describe" to ensure only JSON gets written. See #221. ...

Note that JSON will only get written when no errors occur. Otherwise the output will be the usual error messages.

Add command line interface for managing package overrides.

Refactor runDubCommandLine to use less indentation/nesting.

Only validate (and output warnings) the root package once.

Implement a new dependency resolution algorithm with support for selections. ...

The new algorithm is completely rewritten to be able to find any valid combination of dependencies/versions. The old one could error out in cases where a valid dependency tree could have been built. Now the current selections are also taken into account when invoking without UpdateOptions.upgrade.

Some side changes:
 - Comparing branch versions is allowed now to enable sorting the full set of versions of a package
 - DependencyGraph and RequestedDependency have been removed

Integrate the "dub select" functionality in "dub upgrade".

Make some cosmetic changes to dub version selections. ...

- Adjust code style
 - Let "dub select" output a simple package->version map instead of package->{version, dependencies}
 - Rename dub.select.json to dub.selections.json.

Merge branch 'dustmite'

Preparing dub select command. dub select will select the currently used versions and write them to a file, so that dub can later use this information to rebuild this exact state. This will also be used to override dependencies with either branch versions or not matching versions (to resolve conflicts). (All of this if to be implemented). ...

Other changes:
- Added Version.UNKNOWN, which could be later used for undetermined package versions instead of ~master.
- Added Dependency to/fromJson.
- Added Dependency alias "*" for ">=0.0.0".

Removing superfluous try-catch around dub.remove.

Cleaning up exception handling for dub remove and not catching Throwable somewhere else than commandline.d.

Fix handling of the --local switch. Fixes #259. ...

--local was erroneously doing the same as --system.

Support --combined and --force flags for "dub test". Fixes #247.

Add --force-remove switch and reimplement PackageManager.remove. ...

remove() now first checks for untracked files and leaves the package untouched if it finds some and no force_remove is supplied. This means that after the user gets an error concerning untracked files, it's possible to rerun dub with --force-remove to remove the package cleanly.

Add proper documentation for the "dub test" command. Fixes #83.

Another improvement for the dustmite output match logic.

Silence the "Checking dependencies" message on startup. Fixes #221.

Dustmite: Force a match when a command failed, but the output regex matched.

Only force dustmite match when an explicit failing exit code was requested.

Fix matching linker/program results in dustmite mode and output match status messages.

Avoid copying compiler output files and copy *all* dependencies for "dub dustmite".

Avoid scanning for local packages for "dub dustmite --test-package".

Add a basic dustmite command.

Fix handling of remaining command line arguments (broken by previous commit).

Error out when excessive command line arguments starting with "-" are encountered.