attempt to decompress and manually parse POST body if protocol version 3

This should be compatible with the latest iOS code.  Highlights:

1. Recognizes new HTTP header "Cycleatl-Protocol-Version", which we now set to 3.
2. If Content-Encoding is gzip or zlib, will decompress body before processing.
3. Parses form-encoded-like body manually to extract vars.

You should disable the mod_deflate input filter on your Apache instance.