Remove some commented code
Add a callback for high-level merge in the HTTP server

Currently, the CRUD backend never use the high-level calls, though ...
Simplify README.md
README: "install from source" at the end
Give to [unit IrminMerge.result] its own convenience module

That's IrminMerge.UnitResult

(suggestion from @avsm)
Merge pull request #57 from samoht/master

clean-up before the release