The parser and looking up config keys in the map should both be faster
due to using ByteString.
I had hoped this would speed up startup time, but any improvement to
that was too small to measure. Seems worth keeping though.
Note that the parser breaks up the ByteString, but a config map ends up
pointing to the config as read, which is retained in memory until every
value from it is no longer used. This can change memory usage
patterns marginally, but won't affect git-annex.
While L.toStrict copies, profiling showed it was only around 0.3% of
git-annex find runtime. Does not seem worth optimising that, which would
probably involve either a major refactoring, or a use of
UnsafeInterleaveIO.
Also, it seems to me that the latter would need to read chunks, and
preappend the leftover part to the next chunk. But a strict ByteString
append itself is a copy, so I'm not convinced that would be faster than
L.toStrict.
