Merge pull request #4 from geeknam/master

Allowing a field to be 'dehydrated' with a custom method
Update docs/changelog.rst
Update CONTRIBUTORS.rst
Merge branch 'dehydrate_docs' of https://github.com/geeknam/django-import-export
Merge branch 'travisci' of https://github.com/geeknam/django-import-export
Update travis link
Update import_export/formats/base_formats.py
Merge pull request #9 from tepez/master

supporting both 'extentions' and 'extensions', closes #6
Update CONTRIBUTORS.rst

Add tepez to cntributors.
Add tox configuration
Merge branch 'add-tox'
Update changelog
ADD support for deleting objects during import
Update import_export/formats/base_formats.py
Update import_export/admin.py
Add py27-tablib-dev to tox
Merge branch 'add-tox'
Merge branch 'master' of https://github.com/tepez/django-import-export into xls-fixes
Tweak xlrd loading
Add tests for #d4aa4ed5339ebee8cf1d1c5425fae9473d14bd68