Changed the buildsystem from plain make to SCons.

Advantages:
    - Changes in source files get recognized now.
    - More checks if needed enviroment is installed.
    - check for glib.

Short command reference:

$ scons           # build it all.
$ scons -c        # like make clean
$ scons VERBOSE=1 # Show exact compiler commands
$ scons DEBUG=1   # Enable a debug build.
$ CC=clang scons  # Switch compiler to clang (rebuilds)
$ scons install   # Install rmlint
$ scons uninstall # Guess.

Recommended command:

$ CC=clang scons DEBUG=1

making clean should not be necessary at any point.