CAPI library should be ABI ready

Several things to fix here:

• The library is currently installed without version adornments or ABI tags. It should be installed under an ABI related soname with appropriate symlinks.
• The headers are currently just installed to $PREFIX/include. They should be installed under a path that includes the project name and an ABI suffix, like libmongoc-1.0, etc.
• The header file names, and library names should be made more consistent across the CAPI library, the embedded transport, and their associated headers.
• The symbols in the CAPI header and transport shims should have the ABI version in the symbol names.
• We should provide export macros with the appropriate visibility expansions, and build the libraries with hidden visibility.
• The two libraries should have SONAME and or install_name set with version info appropriately interpolated.