New repos for specs

Hi all,

The chairs have resolved to follow the pattern being adopted by other
groups and use a new GitHub repo per spec.

This will allow you to subscribe only to the repos you want to track.
We will still forward all repo update mails to the mailing list to
accommodate those that are not on GitHub.

Assuming we have no objections on Thursday's call we will move the basic
card payment methods spec and payment method identifiers specs out of the
browser API repo into their own repo and move the SEPA payment methods spec
from the proposals into it's own repo.

We are standardizing on a repo naming convention using the prefix
"webpayments-" and will use "webpayments-method-" for any payment method
specs.

@Mike: Please can you create:

w3c/webpayments-method-identifers
w3c/webpayments-methods-basic-card
w3c/webpayments-methods-sepa

You can migrate the SEPA spec into it's repo before the call as the group
already resolved to adopt this spec.

Question: Would the group like to move the browser APi spec to:
w3c/webpayments-browser-api (or similar) or is this too much overhead and
unnecessary?

Adrian