Charm Store policy updates and refinement for 2.0

[Jorge O. Castro]

Hello everyone,

With 2.0 around the corner we decided to spend some time cleaning up
the page everyone loves to hate, the Juju Charm Store policy:

https://jujucharms.com/docs/1.25/authors-charm-policy

and here is what I would like to propose:

https://github.com/castrojo/docs/blob/master/src/en/authors-charm-policy.md

I've done a few things here:

- I've separated it from one huge paragraph to sections, General,
Testing and Quality requirements, Metadata requirements, and Security
requirements.
- I've split out things that a charm/bundle MUST do and what it SHOULD
do in each section to make it clearer on what is a hard requirement
and what is a recommendation.
- I've removed most of the Ubuntu-specific jargon and generalized it
to include other OSes such as CentOS.
- Made documenting interfaces and external dependencies a requirement.

There are also some new policies that we need ack from ~charmers in
order to implement. Specifically we've made the testing and quality
requirements explicit. I've also added a requirement of using Juju
Resources (which appears to be undocumented?) for payloads.

Recommendations from everyone on what we should include here would be
most welcome, specifically our recommendations around Windows charms
is non-existent.


-- 
Jorge Castro
Canonical Ltd.
http://jujucharms.com/ - The fastest way to model your service