Merge branch 'master' of github.com:munin-monitoring/munin-c
merge COMPILING file into README.md

There is no need to spread the documentation to too many files.
clarify license for all source files

I asked the individual authors about licenses with the exception of
getversion. With that file I assumed the license declaration of the
munin project and used the git history to recover copyright statements.
merge license information into top-level README.md