Compilers: Add arch support for gdc
Merge pull request #324 from opticron/master

Compilers: Add arch support for gdc
Fix orphan format specifier.
Display the compiler binary with invoking the compiler for separate compilation. See #326.
Enable line number display for JSON errors and improve error messages. See #317 and #325.
Ignore any noise on stdout when reading back the platform information.
Display the build date for "dub -h".
Allow empty path nodes. Fixes #177.
Fix up-to-date check for intermediate dependencies.

In a dependency chain with static libraries b and c (a->b->c), changing something in c didn't trigger a rebuild of b, but only of c and a.
Support :subpackage shorthand syntax. Fixes #315.

This works for dependencies, as well as for referencing sub packages on the command line.
Various improvements. Fixes #268.

 - Treat all package paths as ending with a slash to fix path comparison issues
 - Avoid re-reading all packages twice when building, see also #325.
 - Fix bogus "License in subpackage different" warning
Do not store sub packages of "add-local" packages and fix removeLocalPackage.
Avoid the UNC path root "\\" to be part of a relative path. Fixes #302.
Only execute Windows specific unit tests on Windows.
Fix isUpToDate for sub packages
Merge pull request #336 from sinkuu/fix_subpkg_isuptodate

Fix isUpToDate for sub-packages
Use "dub.json" instead of "package.json" in documentation
Use "dub.json" instead of "package.json" when reading from zip archives
Renamed all "package.json" files to "dub.json"
Merge pull request #337 from jrtc27/dub-json

Use new dub.json file everywhere