Add a pkg-config file to the libgroove package

Make the libgroove package install a pkg-config config file to
`/usr/lib/pkgconfig/libgroove.pc`. This allows commands such as `pkg-config
--cflags --libs libgroove` to be executed.

Change the default makefile rule. The rule now executes two commands:

1. Print the currently installed libgroove version.
2. Print the libgroove version advertised by pkg-config.

Bump the PKGBUILD's `pkgrel` variable.