Use CMAKE_FULL_*DIR in pkg-config file

[alyssais]

Otherwise, it doesn't work if these directories are not subdirectories of the prefix.

[gavv]

Hi, thanks for PR!

I guess they should be instead:

• CMAKE_INSTALL_FULL_INCLUDEDIR
• CMAKE_INSTALL_FULL_LIBDIR

(note the placement of "FULL")

[alyssais]

Ah yes, my mistake. Fixed!

[gavv]

Thanks!