Converted git-annex branch access to use ByteStrings, with support also for writing to it using bytestring-builder, which is supposed to be faster. Finished both an attoparsec parser and a builder for the location logs. All the other logs just convert to and from String for now, so there is still a lot of work to do.

The git annex whereis benchmark looks to be around 6% total speedup now, so this only improved it by a few percent, but these little speedups are adding up.

Writing to the git-annex branch may also have sped up significantly; the builder is probably able to stream out to git without doing any internal copies. But there are not many cases where git-annex does a lot of writes to the branch without some other operation that is much more expensive, so I don't anticipate much speed improvement on that side.