installer: Set APP_VERSION from "git describe" if possible

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
readme: List the "More consistent naming" feature last

As is it not so important to the average developer and long to read.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
readme: Add a section about creating mingw-get packages

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>