Restructure support files.

Also removed obsolete project files, as they haven't been updated in
years.
Make it clearer that the spec files are examples.

They are only meant to be used as example files for distros.
Remove Lua < 5.1 code.

We've for some time required Lua 5.1, so any code used for providing
support for earlier versions can be removed.
Fix incorrect characters.
Update outdated README text.

In the process also switch to Markdown from Lyx as it's much more
suitable for the kind of text we supply.
Update doxygen file to newer version.