RXMapBlock/Function take stop flags to indicate that iteration should be halted.
RXConvolutionBlock/Function take stop flags to indicate that iteration should be halted.
Folds can be terminated early.
Filters and linear searches can be interrupted.
Tests that filters stop iterating correctly.
Removes the filter/map functions since the blocks do the job.
Merge branch 'feature/interrupting-higher-order-functions' into develop