FIX: Calculate and test some inital conditions
FIX: Missing gain
ENH: Remove k
STY: Better comment
ENH: Better testing
ENH: Better coverage
FIX: Fix test
ENH: Working zpk2sos, better tests
STY: Cleanup
STY: Cleaner [ci skip]
STY: Comment about tests [ci skip]
FIX: PEP8 + old numpy
STY: Clearer n_sections
FIX: Dont use newaxis
ENH: Add example
FIX: Fix gain