Source files are now collected at a central place instead of in every generator. ...

Package.getBuildSetting() now determines all source folders and recursively collects all source files there.

Implemented pre/post commands and --build=ddox + support "sourceFiles". ...

Other fixes:
 - fixed class Dub to work with other path than cwd
 - "files" has been deprecated in favor of "sourceFiles"
 - --build=docs also works now
 - Changed the way build flags are parsed (instead of checking every possible field for existence, all fields are iterated and their name is matched)

Renamed all the "vibe" package to "vibecompat" to avoid conflicts.

Added rudimentary support for the --arch= option and moved build type flag generation to a common place.

"dub build" and "dub run" are now also executed using the generator system (RdmdGenerator).