Description

Currently RNP_LOG prints the whole path to the source file, i.e. in my case:
[process_pgp_source() /Users/aaaa/bbbbb/rnp/src/librepgp/stream-parse.cpp:2983]
However it would be better to hide prefix, i.e. print just the following:
[process_pgp_source() /librepgp/stream-parse.cpp:2983]

The best way I see right now is to use some build-time define with prefix path length, like it described here: https://stackoverflow.com/a/40947954/452752