Allow the use of shorthands using ${prefix} for exec_prefix, and
${exec_prefix} for includedir and libdir, which makes the generated .pc
files a bit cleaner and more flexible.
Some packages might have some parts that are built for certain build
configs, meaning that they could have .pc files of their own, such as
Pango, where PangoFT2 is optionally built. Allow such an option if
needed.
Also remove some trailing whitespaces.
Add a generic script, pc_base.py, which can be utilized to obtain path
info, along with user-input version info, which can be used to generate
pkg-config .pc files. Also enhance replace.py a bit so that it can also
be used in the future to replace multiple items in a file in one shot.
This is done to make building introspection files easier, as it depends
much on the pkg-config .pc files to work.
Update the project files so that when Python is available, we can generate
the full, usable .pc files when we complete and 'install' the builds, and
copy them to appropriate locations so that pkg-config can be set to find
them easily.
