* Add support for CouchDB 1.5.0 in unit tests, drop support for CouchDB 1.2.0
* Now Build-Depends and Depends on `couchdb-bin` >= 1.5.0 as we'll no longer be testing with CouchDB 1.4.0
* Tweaks to usercouch.ini CouchDB config:
- No longer overriding anything in [replicator] section as CouchDB defaults seem good here
- In [database_compaction], up `doc_buffer_size` from default of 512 KiB to 4 MiB; this results in smaller databases, and also seems to make compaction far less prone to retry during high DB load
- Also in [database_compaction], up `checkpoint_after` from default of 5 MiB to 16 MiB
- In [compaction_daemon], lower `min_file_size` from 4 MiB to 1 MiB (default is 128 KiB)