Mailprocessing

* imapproc: fix crash when attempting to query message flags on empty folders
* maildirproc: catch and log ENOENT when moving to a nonexistent target folder
* maildirproc: logging improvements/fixes
* maildirproc: fix handling of '/' as separator
* Various test fixes and flake8 cleanups (test suite still non-functional)
* Fix clean target in Makefile on MacOS

- Added example logrotate configurations
- Added SIGHUP handler for reopening log files (useful for
log rotation)
- Use locking for PID and log files. You need to specify
dedicated PID and lock files if you want to run multiple
concurrent imapproc processes.
- Write PID file
- Improve signal handling and cleanup after receiving fatal
signals. Continuous mode in particular is a lot more
reliable and predictable now.
- Download message headers in a batched manner
- Download message flags in a batched manner
- Various documentation and release engineering fixes/cleanups

- Replace setup.py templating by static setup.py

- Fix all target in Makefile
- Major documentation overhaul: converted documentation to RST and introduced
pandoc based build for HTML documentation and manual pages.

- Add medium.rc sample RC file (examples for some of the newer functionality)

- Fix issues/2: header caching in continuous mode will now refresh the cache
after every sleep(). Previously it didn't and the cache went stale.
- Working SSL certificate validation and --insecure option to bypass it
(contributed by Mark Yen)
- Python 3.4 compatibility (contributed by Mark Yen)
- Add fault tolerance for decoding errors to header parsing code