added a basic bitcoin gateway with an example

add a stub bitcoin backend
added bitcoin gateway, stubbed views
added basic example templates
redirect back if not ready
my html is really bad
show failure reason
cleanup
added minconf, sane defaults for settings
added a retry button
removed unused form
calculate sum based on txns
clear session if done
updated docs
added tests
Fixed the usage of the paypal integration.
Refs #47. Clarified in the documentation that the RECEIVER_EMAIL should be declared twice.
Merge wepay changes from @krotkiewicz.
Ability to use payment tokens. Changes from @dstufft
Add multiple merchant account support. Changes from @paltman.
Merge pull request #45 from agiliq/bitcoin

Added a basic bitcoin gateway with an example. Thanks @tuxcanfly.
Added the names to the CONTRIBUTORS.txt for latest contributions.
Updated the changelist with upcoming changes.
Added a reference to the bitcoin doc in the index.rst.
Added bitcoin.rst in gateways section.
Fixed a typo in the google checkout docs

Fixed a typo in the google checkout docs that referenced worldpay instead of google checkout. 
Also added a missing import to the urls.py example.
void referenced undefiend variable 'money' that it didn't need
Google Checkout: Added Shipping support to Google Checkout. Currently supports flat-rate-shipping, merchant-calculated-shipping and pickup, doesn't support carrier-calculated-shipping yet. I also updated the google checkout documentation to reflect the change, and added some tests. Added my name to CONTRIBUTORS.txt while I was at it
Google Checkout: Added ability to capture the private data on an item when they send it back
updated the docs a little
Merge pull request #48 from kencochrane/patch-1

Fixed a typo in the google checkout docs
Added Ken Cochrane to the list of Contributors. Thanks @kencochrane
Merge pull request #49 from mattmcc/master

void referenced undefined variable 'money' that it didn't need
Added Matt McClanahan to the list of Contributors. Thanks @mattmcc