Switch to argparse

This fixes #98.

Also remove "fix_string()" in preparation for 1.0.
Format
Add missing parentheses
Format
Move argparse import to the function scope
Simplify
Sort listed fixes
Describe fixes in more detail
Regenerate readme switch change to argparse
Relax help test
Simplify
Improve test coverage
Improve test coverage
Remove unnecessary code block
Add "--indent-size"

This is related to #99.

This causes test failure in
"test_trailing_whitespace_in_multiline_string()". Do not merge until
test is fixed.
Avoid touching trailing whitespace in Reindenter
Ignore temporary Vim files
Document "--indent-size"
Reindent

pep8 alone did not detect this.
Add documentation