fix bonus status code (should be 7) and counterbalancing criteria
added to bonus status code fix
fixed typo from earlier commit
subtle change in command docstrings to fix hit expire

docopt wasn't parsing command as expected, causing all "hit extend"
commands to extend assignments, not time. Added parentheses around
pairs of optional parameters that have to appear together to fix the
problem.

Fixed similar problem in worker list, though don't think earlier version
caused problems in this case.
fix bonusing issue

If multiple workers tried same assignment, only gets database entry for
the one who completed the hit

Conflicts:
	psiturk/psiturk_shell.py
switch to gnureadline
changing instructions to reference gnureadline
accommodating full version number (with minor changes)
update to contributors guide to mention pull requests going to dev
stepping version number
Merge remote-tracking branch 'origin/2.0.1_fixes'

Conflicts:
	psiturk/version.py