Renamed libs directory.
Merge pull request #23 from jgmdev/premake

Refactored wx.feature.
Moved port dirs in a new toolkit dir (e.g. require wx.toolkit.gtk), moved setup.h dir creation in setup.lua, added temporary functions to copy setup.h in the right place, added bin dir for binary projects (e.g. wx-config, wxrc).
wxMedia setup, moved setup.lua before configure.lua (maybe should be added later as last script before bins and libs).
Added os.host() to premake.
Changed wx.scandir to use os.host().