Remove unused directory creation
Move libtool and ninja exection into exec_XXX functions to easily change argument sets
Define WEBRTC_TARGET as a variable to more easily alter build target
Run 'strip' when making Release builds to remove un-needed symbols and significantly reduce the size of resulting static library
Merge pull request #38 from talko/striprelease

Run 'strip' when making Release builds to remove un-needed symbols an…