Implemented test conditions and simple assertions.
Integrated assertions into the main test files.
Added custom assert definition facility.
Added special assertions.
Added comparison assertions. Refactored other othes.
Added exception assertion.
Added constraint-based assertions (`assert-that`).

Condition object tests are still failing. I'm thinking of what I
really want to put into condition object for assertions.
Fixed condition objects of `assert-that`. Added object override.
Merge branch 'assertions'