Add a `__main__.py` file to the top directory

Makes it easier to use the tool directly from a checkout.
'sep' is not used by the print fixer

Should raise coverage of fix_print to 100%
Drop a check in fix_next for an empty base

Since the matching rule is `base+` there will have to be a match for
something.

Should make coverage for fix_next 100%.
add tests for fix_map

Along the way discover an unnecessary limitation in the pattern.
test fix_map w/ kwargs
Rename a test to make its purpose more obvious
Add test_fix_filter

Along the way fix the pattern from being too broad (filter only accepts
2 arguments).
Add tests for fix_zip

Discovered the pattern was too restrictive in some senses — e.g. didn’t
allow for the empty call which is legal — and too loose — e.g. allowed
for keyword arguments.
add tests for fix_raise
Add tests for fix_metaclass

Include a fix for the one-liner case.
Tests for fix_dict
Add a fixer for basestring

As part of #31
Add a missing comma
Add basic tests for libmodernize.fixes
Remove unnecessary import
Add tests for fix_range

Currently failing due to lib2to3.fixes.fix_range being used.
Turn off lib2to3.fixes.fix_xrange

Allows fix_range to do all the work (although it’s still failing its
new tests).
Get fix_range working

Had to simplify the pattern in the fixer as I just couldn’t get it to
work with a single argument while also working with 2 or 3 arguments.
Merge pull request #48 from brettcannon/fix_basestring

Add a fixer for basestring
Merge pull request #49 from brettcannon/add_missing_comma

Add a missing comma