Python 2 compatibility

You can easily run into problems, particularly around dependencies
if you try to import the package to be installed inside of your
`setup.py`.  Instead, use `pkg_resources` to get the version
without importing.

This technique and the hazards of importing are discussed here:
http://stackoverflow.com/a/2073599/386210

six is imported, but not listed as a dependency in setup.py.  Add it.

Fix setup

It avoids having to read an extra VERSION file in the module code itself
and leaves all the ugliness in setup.py, where ugliness belongs. This
is the same technique that the requests module uses.

This should work on any version of Python >= 2.6.

Read the __version__ from the fitparse/__init__.py without importing it

Split bytes with bytes, not with string