do not create a new error
added basic test for continuous assertions
added basic implementation of continuous assertions
include experimental_test in test suite
revert on invalid assignment
tests for assertions on complex object
test for multiple assertions on a single variable
added tests for trigger mechanism
added TriggerSolver
added tests for layer activation
added simple  layer activation implementation
added postponeEnabling flag to cassowary
added tests for scoped constraints
added first implementation of scoped constraint
added postponeEnabling flag to DeltaBlue
added tests for scoped assertions and triggers
scoped assertions and triggers
adjusted tests to check for a more convenient api
check for additional flag allowFailing
set new flag allowFailing and attach test function to external constraint