add redcarpet markdown processor

* this is for rendering of Requirement descriptions
seed Requirement model from PCI Standards csv file
render requirement description using markdown
Merge pull request #21 from akshatpradhan/seed_requirements

seed Requirement model from PCI Standards csv file
refactor proof for user view

* proof for user view moved to requirements#index
* replace create with build in `proofs_controller` to stop writing to
database twice
* change redirect page to `requirements_url` after sign in
* move marketing copy from requirements#index to home#index
* add navigation link to go to requirements#index for user
* fix homepage integration test
Merge pull request #30 from akshatpradhan/move-requirements-view

refactor proof for user view
user updates proof for requirements

This feature allows the user to update the the image of a proof for a
requirement.
Merge pull request #31 from akshatpradhan/proof_update

user updates proof for requirements
unignoring .rspec, add format doc
Merge pull request #35 from akshatpradhan/rspec-improvements

unignoring .rspec, add format doc
change license to AGPL-3.0

* update README.md
change copy for home page and requirements page
Merge pull request #37 from akshatpradhan/copy_changes

change license and copy changes
improve home page image

* No change request required for copy/change
make license more readable

* doesn’t need a change request
change marketing copy on home page

no change request needed for marketing copy change
add link to forum and PCI Assessment page
move requirements csv into subdirectory of db/

no change request needed as this is small cleanup code.
remove rails 2.3 style plugins in vendor/

This fixes `DEPRECATION WARNING: You have Rails 2.3-style plugins in
vendor/plugins!` message when deploying to heroku.
fix github login for unnamed users