by one -> SHOULD, not MUST
removed increments by 1
Merge pull request #118 from Tieske/increments

increments by one
Mark 2.0.0 as RTM
Merge pull request #120 from mojombo/release-2.0

Mark 2.0.0 as RTM
Add BNF Grammar for valid version strings

Written in collaboration with @petermichaux

Closes #110
Improve BNF grammar

Better names, more intuitive ordering.
bnf: Simplify 'alphanumeric identifier'