add travis settings

This adds settings to test for python 2.6 and 2.7 and
django versions 1.3, 1.4, 1.5 and 1.6.
add travis status image to README.rst
correct syntax on status image in readme
remove version nr from libboost-python-dev in travis configuration
remove python 2.6 from .travis.yml
Merge branch 'travis' of github.com:relekang/sorl-thumbnail into relekang-travis

* 'travis' of github.com:relekang/sorl-thumbnail:
  remove python 2.6 from .travis.yml
  remove version nr from libboost-python-dev in travis configuration
  correct syntax on status image in readme
  add travis status image to README.rst
  add travis settings
Add some authors mention
Merge branch 'relekang-travis'

* relekang-travis:
  remove python 2.6 from .travis.yml
  remove version nr from libboost-python-dev in travis configuration
  correct syntax on status image in readme
  add travis status image to README.rst
  add travis settings