Latest version of charter

Hi all,

I have pushed the latest version of the charter to GitHub and you can view
it here:
http://w3c.github.io/webpayments-ig/latest/charters/payments-wg-charter.html

I have tried to incorporate changes from all of the discussions over the
last week of calls and emails.

Highlights:

   1. Dropped "architecture" from the WG name
   2. Move wallet section out of scope and goals.
   3. Some changes to wallet section to ensure it is not restrictive on
   what the "wallet service" could ultimately become.
   4. Add registration to the set of standards
   5. Added an optional deliverable for a generic card payments scheme
   (i.e. a specialisation of the messages and flow specifically for cards)
   6. Emphasis on standardising a high-level flow and message format with
   separate deliverables focused on standardised delivery mechanisms in
   different scenarios (i.e. WebIDL, REST and optional inter-app comms on
   mobile).
   7. Lots of wording and formatting tweaks.

I haven't had a chance to go through Nick, Zak and Pat's comments in detail
yet. I'd appreciate it if you guys could review the latest version and let
me know if any of your concerns are addressed. I will do the same but we
may not agree :)

Adrian