added overarching but simple integration test for cyclopts
renamed integration tests to properly reflect that they are in fact testing the cbc solver. updates cbc solver documentation.
made variable tests less namespace verbose
made addconstituent public, removing need for friend class
updated solver interface documentation
prepended cyclopts to test name for easy regexp selection
added tests for the function base class, updated documentation, and made slight API changes based on documentation
made constraint iterator access const as it should have been
added tests for objective and constraint functions, updated documentation
finished variable-related tests, updated related api, and updated documentation. this last commit closes all code-related issues in cyclus/cyclopts#37.