Add new 2015.8 Windows repo settings mentioned in main documentation

[myii]

Some of the new Windows repo settings have been addressed by PR #205. During that process, identified a number of new settings that have yet to be transferred to this formula. Copying over those findings to this issue so that these can be addressed someday.

Settings still be transferred from the documentation

There are still some new settings mentioned in the documentation that could be transferred to this formula:

1. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-provider
2. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-branch
3. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-ssl-verify
4. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-user
5. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-password
6. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-insecure-auth
7. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-pubkey
8. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-privkey
9. https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-passphrase

[myii]

For anyone who gets around to addressing this issue, it's worth noting the following point.

https://docs.saltstack.com/en/latest/ref/configuration/master.html#winrepo-authentication-options:

Winrepo Authentication Options

These parameters only currently apply to the pygit2 winrepo_provider.

So that refers to settings 4-9 in the list above.