Implement commit message grader with first validations

* Validates if first letter is lowercase

* Validates if there are redundant blank lines (no spec)
Add more validations to commit message grader

* Made the redundant empty line validator working & added spec

* Added trailing whitespace validator with spec
Add more validations to commit message grader

* Added line_leading_whitespace and line_too_long validators and
  relevant specs

* Reference commit not working due to punctation treated as wrong
  leading whitespace
Add punctation validations to commit message grader

* Checks for leading whitespace and separating line in punctation

* Relevant specs added

* Proper punctation detection fixes previously non-working specs
Merge branch 'master' of github.com:visualitypl/codegrade