Added the possibility to specify "dflags-xyz" in addition to "dflags" for platform specific flags. ...

Can be one of:
 - dflags
 - dflags-platform
 - dflags-architecture
 - dflags-platform-architecture

where platform is "windows", "linux", "posix" etc. and architecture "x86", "x86_64", "mips" etc. (the lowercase version of the predefined D versions)

Note that the platform is currently hard-coded to windows-x86

All dub specific files are now stored in a .dub subfolder.

Removed the shell/batch scripts and modified dub to be a stand-alone executable. ...

Also removed all implicit dependencies to vibe.d (such as always specifying the vibe.d source folder using -I).
Fixed expanding of packages with multiple package.json files (the top-level folder inside of the zip archive was detected wrongly).

Added missing file.