Compute response of filters
Fixed import warning
Incorporate feed back from simonster

All functions can take and ```Filter``` type.
Fixed indentation.
Use ```AbstractVector```.
Use list comprehension.
Don’t return frequency.
Run tests.
Change to freqz/freqs
Combine two hz functions using Union type
Removed return command
Merge pull request #32 from codles/master

Compute response of filters and test against matlab freqs and freqz