In case PYCAIRO_NO_IMPORT is defined we declare the api struct as extern and hide the
import function. Also don't make the API struct static so we can access it from outside.
Pycairo installs .pc files which work quite well where the default
prefix is used, like with distro packaging etc. In virtualenvs
the pkg-config look up path needs to be set manually, and in pip
wheels are involved, where we had to disable installing .pc files
as they can get reused for a different prefix.
To make it easier for other python modules to use the C API introduce
a new function get_include() (similar ot what numpy has) which returns
the include path that needs to be passed to the compiler.
Since we can't really get the old header install path from the module
(one could walk up the tree and look for matching files, but that's ugly)
move the header file into the package itself, so that the path can be
dervived from the package path.
To prevent code from breaking which hardcodes the old include path
install a header to the old location which includes the new header
location.
Christoph Reiter