Improve exported ABI interface decription

Add VERSION and SOVERSION numbers to describe library API/ABI.
Leave commented for now because they don't fully work on OSX yet.

Add debug postfix to allow ABI incompatible debug/release libs
to be distinguished.

Export targets to build directory, making build directly usable by
client projects without installation. Add relevent target include
directories to enable this.

Add example of COMPATIBLE_INTERFACE property by API/ABI checking
by clients.