Update supported countries
Update README with latest gateway metadata

Also adds a rake task to spit out the gateway listing in Markdown.

Closes #829.
Moneris: Allow CVV to be optionally passed

Only certain account types at Moneris allow a verification_value to be
specified.  By default, we don't pass it.

If you have an account that allows the verification_value, you can
specify that when you instantiate the gateway.

Closes #843.
add more of stripes supported countries
Cybersource: Remove email requirement

No longer raise an ArgumentError when email isn't specified.  Instead
let the gateway itself complain if that's required.

This makes the code for Cybersource more consistent with the other
gateways.

Closes #849.
Merge branch 'master' of https://github.com/Shopify/active_merchant