Clearly separated fetching (physical reading) from decoding phases (data
interpretation). Threaded fetching added but disabled as needs more work for
Windows. For Linux needs some touches to add pthreads if this is enabled,
probably with a compile-time switch.
The code reorganisation makes it easy to add also async API, similar to
cURL's one.
- Fix BIT problem for BIT values represented with 5 bytes. Typo.
- Make it possible with an ini variable to switch off/on statistics
collection.
- Compile-out debug checking of uneaten data from the line, when the
build is release. According to callgrind this was eating some percentage.
