correct imports

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".

Not catching Throwable when metadata is fetched. ...

Documentation updated.

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

Improve wording.

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

Fix typo.

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.

Improve error messages for errors during package removal.

Improve error message in case of missing packages.

Output errors the occur while fetching package information as diagnostic output. See also #236.

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

Add Dub.overrideSearchPath to define a single and only path that is searched for packages.

When inferring the module name from the file path for "dub test", use the longest matching import path instead of the first match. ...

This fixes the inferred module name in case of multiple overlapping import paths.

Only copy DDOX resources if newer on Posix.

Make "dub.json" the primary choice for a package description and handle "package.json" as a fallback.

Don't include package.d modules for "dub test". See #198.

Determine proper module name for "package.d" files and "dub test". Fixes #198.

Implement individual building of dependencies.

Add support for "add-local" without version name.

Fix assertion errors when the HOME variable is a relative path.

Add an "allModules" tuple to dub_test_root and pass it to runUnitTests or the "tested" code.

Rename the generated root module for "dub test" to "dub_test_root". ...

This is clearer than test_main (after all, it doesn't necessarily contain 'main()') and also reduces the risk of name clashes.

Avoid casting RegistryPackageSupplier[] to PackageSupplier[]. Fixes #186.

Fix path separators for DUBPATH.

Make "dub test" work for library configurations without a "mainSourceFile".

If --main-file was given for "dub test", prefer a normal library configuration over a "unittest" one.