Create standard way to designate intended milestone and API in issue subjects

[jfh01]

Because setting an issue/PR milestone and label requires write access to the repository, issues submitted by general contributors won't start with either milestone or label attached.

Suggest that we establish a standard designation in the issue title to indicate which version and which API an issue/PR is targeted for.

Issues titles would be prefixed with [version / API].

For example:

[0.3.1 / agency]
[0.4.0 / provider]
[provider] (for an issue/PR that does not yet have an intended version.

If folks agree with this approach, would need to update CONTRIBUTING.md and create issue templates for the repository that guide people to use the correct designation.

[hunterowens]

Perhaps we should just have people submit - something like

[ ] Breaking 
[ ] Non-Breaking 
[ ] I'm unsure 

in each issue, allowing them to tag the info that the maintainers need for clarification into milestone + labels.

[jfh01]

Closing this issue to be worked on #286.