Added theming

[DeliciousHair]

This is a rather large change in terms of the amount of code affected owing to it proving rather difficult to add this feature into things in a reasonable manner. The following changes have been made:

• collect all plotting functions in a single class, where theme is defined at instantiation
• all uses of the grayscale keyword have been either replaced with theme or removed as appropriate
• the options keyword has been removed from qs.html()
• as well, the download_filename keyword has been replaces with html_filename
• type hinting was added to all code touched
• all non-conventional import statements have been made conventional
• the 'Known Issues' segment of the README has been removed as the issue is no longer present

To use theming, a the current default and grayscale themes have been provided in _plotting/themes.py. Any user-defined theme can be be created by following the dictionary structure provided, noting that all keys must be present or the behavior is to fallback to default

[ranaroussi]

Not sure why you had to rename the imports. The _ prefix was there to indicate that this is a dependency module. Otherwise - I like the idea of using themes but cannot approve the PR as it.

Can you create a new PR with only the theming option and without any backward compatibility-breaking changes?

[DeliciousHair]

Hello!

The renaming was because underscore hiding all the module names is very unusual, and was making the code more difficult to read IMHO. As for adding this without the non-breaking changes, short answer is not really. The issue is that the functions as-is are set up in a manner that is not terribly amenable to a (consistent) theming scheme, as can be seen from how the grayscale value is used over and over with varying if-then statements throughout. Putting the theme definition into a (rough) class as I have has fixed this issue, but forces the changes to the function signatures as I've done in core.py and wrappers.py; the user-level use of everything remains unchanged in terms of what functions are called and how the module is organized, while only the function signatures have changed.

I could, however, include deprecation warnings in said functions; that would be possible and reasonable.