Document coding, testing, and process standards
Simplify review section of contributing doc.
Add prose documentation requirements and issue completion condition requirements
Remove test method name caveat to be discussed in a different issue
Merge pull request #6 from twisted/contributing_doc

Document coding standards, testing standards, and contribution process

Reviewers: @tomprince, @exarkun
Fixes:  #5

Added a contributing doc outlining the coding standard, testing standard, and review and merge process for the vertex project.