Property cycle support for "stem", "step", "vlines", and "hlines"

[lukelbd]

I'd like to add property cycle support for alternative line-plotting commands, namely stem, step, vlines, and hlines. Since these are just alternatives to simple plot line plots, I think it makes sense for them to use the property cycle.

The implemenation would be similar to how property cycle support is added to Axes.scatter via cycle_wrapper in proplot/wrappers.py.

https://github.com/lukelbd/proplot/blob/92d4d84b467d2ef9a4a081c7bcf4246ca91f3df8/proplot/wrappers.py#L1357-L1370

[lukelbd]

Turns out step had been already supported for quite a while, but #166 adds support for flexible arguments passed to vlines and hlines (previously they required 3 arguments, like fill_between), and suppresses a deprecation warning in stem.