DOC: Update haroldpolyadd function

[whzup]

Updated the haroldpolyadd function. It now trims the zeros of the output instead the zeros of the input. Improved the docstring with a parameter and return list.

If you like these changes I can change the haroldpolymult function as well.

[ilayn]

Just to clarify, do you want to trim the input or output or both ? I am wondering if all options should be exposed with trim_input and trim_output.

The use cases are (as far as I can see):

• Trim input: The inputs can be zero padded at the front but output should be whatever the trimmed sizes are Example [0, -2, 1, 2] and [0, 2, -1, 1] -> [0, 0, 3]
  • Trim output: The inputs can be zero padded at the front but output should be trimmed Example [0, 0, 1, 2] and [0, 0, -1, 1] -> [3]
• Trim input and output: The inputs can be zero padded at the front and the output should be trimmed Example [0, -2, 1, 2] and [0, 0, 0, 2, -1, 1] -> [3]
• Don't touch anything (both false): Example [0, -2, 1, 2] and [0, 0, 0, 2, -1, 1] -> [0, 0, 0, 0, 0, 3]

[whzup]

Hmm, well the question is whether or not one or the other is necessary 🤔 Although, if you provide default True's it might actually be no problem. Both would do it as well 👍

[ilayn]

I played with different versions and it has a bit of effect on the rest of the library since I do a lot of stuff regarding the MIMO transfer functions. Hence it is a bit of a bigger surgery.

Do you mind keeping this PR to the docstrings?

Then it is easier to chop the rest into smaller pieces later.

[ilayn]

@whzup Sorry it took a while to spare some time for this. Now it should be a bit better to work on. I've enabled the intersphinx extension to link automatically to Numpy.

[ilayn]

I've closed and opened to try to trigger Travis,

[ilayn]

All green. Merging. Thanks @whzup !