Replace existing templates with github templates

[brianraymor]

The current RFC process is modeled on Python PEP and Rust RFC. Both have steps which manually copy a template:

Copy 0000-template.md to text/0000-my-feature.md (where "my-feature" is descriptive. don't assign an RFC number yet).

@kislyuk has suggested that both the charter and RFC process could be simplified by using a standard github template with inlined information from the RFC or charter process to walk submitters through the dance steps.

[Bento007]

Relates to #122