New .travis.yml for travis CI

Add requirements files to ease pip installation.
rm simplejson requirement
fixed super call in Resource.datatype()
project.parent() returns None instead of throwing KeyError
Merge pull request #35 from pyxnat/travis

New .travis.yml for travis CI
Merge pull request #36 from rherrick/master

Add proxy support to Interface class
Merge pull request #37 from karchie/devel

fixed super call in Resource.datatype()
BF: python < 2.7 compatibility -- use explicit set([...])
Merge pull request #38 from neurodebian/master

BF: python < 2.7 compatibility -- use explicit set([...])
update for py3k

Fixed the following syntax issues across repo:
- print statement -> print function
- import StringIO -> import io.StringIO
- StandardError -> Exception
- exception <Exception> as ...
- urlparse -> urllib.parse.urlparse
- httplib.HTTPConnection -> http.client.HTTPConnection
Merge pull request #39 from pyxnat/py3kfix

update for py3k