Parametrise installation

[Doeme]

It would be neat to have the installed files parametrised, s.t. the scripts and buildroots can be installed into an arbitrary directory.
Maybe a Makefile would be a neat way to do this, which preprocesses e.g. gebuild.m4 with the m4 macro expander.

[TheChymera]

That's a good idea, do you think this could be used to allow unprivileged users to create subsystems (also addressing this concern)?

[Doeme]

Even though we said we'd concentrate on other things, since the manpages will be generated during install time by looking at the docstrings in the scripts/**.sh, we will need a makefile anyways.

This has been added in 424d741, hence I am closing this commit.

@TheChymera You will need to update your personal -9999.ebuild, look into the .gentoo-directory for guidance (you should probably just copy the file, minus the src_unpack and plus some inherit git-r3)