Merge branch 'release/0.2.0' into develop
Merge branch 'hotfix/0.2.1' into develop
avoid checking certain contracts in exceptional cases
updated comments for test cases
Merge branch 'feature/except' into develop
enforcing the base class invariant in the derived class contract
better doc for the derived class contract and a test stub
derived class contract tests
Merge remote-tracking branch 'origin/master' into feature/derivedclass

merged contributed changes in README.md
README.md changes

removed github syntax highlighting because it doesn't work with other markdown viewers
added the description of the derived class invariant block
removed limitation of the contract is the derived class
added derived class contract to the list of supported contract block types
minor typo
fixed the derived class contract for the case when a base class doesn't have a class invariant contract
fixed typo
Merge branch 'feature/derivedclass' into develop
bumped the version to 0.2.2
Merge branch 'release/0.2.2'