Merge branch 'release/v0.3.6' into develop
fix: silent fallback for ambiguous files not working for some files

the silent fallback doesn't work for po files that start with the full
name of the language
fix potential race-condition in compile_po

processing of po files might not in all cases finish in order. So it is not
enough to check for the "last" file to be processed, but the number of
processed files is important. The task is done, if all files have been
processed.

Unfortunately it's hard to test this behaviour. May be, some day a decent
test-case can be written. For now I don't have the time.
bump version to 0.3.7 and update readme
Merge branch 'release/v0.3.7'