prune trailing whitespace
fix syntax
rename substitution -> formatting
and example of using a dict as kwarg
fix syntax
fix typo
docopt has entered the arena
fix missing s
fix prompts in exceptions examples
prune some more whitespcae
fix a typo
move example to warning section

These examples are part of the warning about mutable keyword arguments, so make
them appear in the warning box.
Merge pull request #97 from esc/tweak-intro

Tweak intro