Organize into a real installable module

[endolith]

@nschloe if you have an idea how to arrange this, go ahead. The only installable module I've made is https://github.com/endolith/waveform_analysis (everything else is single-file gists and the like)

[nschloe]

Sure thing. You want to stick with complex_colormap as a name?

[endolith]

Well can you think of any other name that would be applicable to a few different variants, and functions for plotting in a few different ways?

[nschloe]

Not sure what you mean exactly. We can always change it later.