publish 'build.version' and 'build.version.formal'

See http://confluence.jetbrains.com/display/TCD7/Build+Script+Interaction+with+TeamCity#BuildScriptInteractionwithTeamCity-AddingorChangingaBuildParameter
Merge pull request #104 from Albacore/feature/ext-tc-version

publish 'build.version' and 'build.version.formal'