update from deprecated testing assertion
break out live session testing utilities to mixin
fix exception while using default teletype delay

Without setting a teletype delay, an exception, "TypeError: unsupported
operand type(s) for /: 'NoneType' and 'int'" was raised.
fix exception raised calling enter() without keys

Calling Session.enter() without a `keys` argument raised "ValueError:
need more than 1 value to unpack".
add test suite for prompt wrapper

Calling a prompt-decorated method raised "ValueError: need more than 1
value to unpack".
remove keys from prompt message when not provided
treat subprocess output as bytes, not strings
for Python 3
add Python 3 friendliness to the session example
remove quotes from session info in prompt message

Quotes and brackets together seem excessive.
formalize Python 3 and Python 2 testing apparatus
add meaning to testing strings
added `enter`'s `teletype` parameter to docs list
upgraded to docutils 0.11
add GitHub issue linking shortcut to the docs
add list of v0.3 changes to docs
bump version number
handle unsupported spelling extension in Python 3
add missing files to MANIFEST.in
(thanks to check-manifest)
Merge branch 'release-0.3'