Implemented basic build platform detection and extended the possibilities for platform specific fields in package.json.
Renamed everything "vpm" to "dub".
Fixed upgrading/install logging of ~master dependencies.
Implemented some standard build configurations.

If DFLAGS is set, dub will print now that it's building the $DFLAGS configuration.
Merge branch 'master' of github.com:rejectedsoftware/dub