Truncate long filenames on extraction.

Closes chfoo/warcat#5
Keeps partial extract on IncompleteRead.

Closes chfoo/warcat#6
Bumps version to 2.3a1
field.py: Uses more pythonic conditionals for lists
Only check and warn block length during verify command.
Merge branch 'develop'
Bumps version to 2.2.3