Add license text to fdup.1

This way, I comply with my own license which requires distributors of binary
code to replicate the license text inside the documentation.
Rework source tarball rule

There is a target tarball now that will automatically generate a tarball with
a suitable name. Also, we use git describe to generate a revision name now.
This is far more reliable than git rev-parse as it automatically incorporates
the name of tags.
Move source files into src directory
Do not put git specific files in tarballs
Add installation instructions
Merge branch 'dev'
Update README
Add CHANGELOG