[paymentrequest] First set of API refactoring changes. (#26)

This pull request includes refactoring of the API to simplify payment request code (for example, by removing the double promise call). It also addresses important comments made in issues #15, #18, and #23.

This is the first in a set of refactoring changes to incorporate feedback we have received.
You can view, comment on, or merge this pull request online at:

  https://github.com/WICG/paymentrequest/pull/26

-- Commit Summary --

  * Refactor the API to eliminate the double promises.
  * Added code example for constructing PaymentRequest.
  * Rename PaymentInstruction to PaymentResponse
  * Add complete and abort methods to PaymentRequest.
  * Add state transition model and attribute.
  * Added headings for the PaymentRequest interface elements.
  * Add a CurrencyAmount dictionary.
  * Added more information about the proposed delegated state.
  * Delete note about issue #15.

-- File Changes --

    M specs/paymentrequest.html (479)
    A specs/state-transitions.svg (98)

-- Patch Links --

https://github.com/WICG/paymentrequest/pull/26.patch
https://github.com/WICG/paymentrequest/pull/26.diff

---
Reply to this email directly or view it on GitHub:
https://github.com/WICG/paymentrequest/pull/26