Refactor Parser into Loader

[mayfield]

• Parser.parse -> Loader.load
• Parser._parse ->Loader._load`
• Use pytz.open_resource for zone file loading to fix pytz installs
  using shared zoneinfo files.
• Fix for python2 setup and test (backport FileNotFoundError name).

Tested on Fedora Core 24 (linux), python2.7 (distro), python3.5
(distro)

Fixes #34

[sdispater]

Thanks. Looks clean :-)

Just a quick question though: why did you put

try:
    FileNotFoundError
except NameError:
    FileNotFoundError = IOError  # py2k

in setup.py?

I just tested without and it works fine, but I'm on OSX so there might be some issues on Linux systems that require this.

[mayfield]

FileNotFoundError is only available on python3. Actually only on 3.3+ I think. How it would be available otherwise is beyond me. Here is output from my osx box...

:; python
Python 2.7.12 (default, Jul 30 2016, 08:56:53) 
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> FileNotFoundError
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'FileNotFoundError' is not defined

Same error. I ran into this when doing python ./setup.py test from linux btw.

[sdispater]

I didn't know and I was not getting the error because I'm not using python setup.py test but I directly invoke py.test