Add parameter command to Button

[LondonClass]

Should I promote this to hover method? Or promote it to other elements?

Use Cases:
(1)hello_button = UIButton((350, 280), 'Hello', command=lambda _: print("hello"))

(2)command_dict = {pygame_gui.UI_BUTTON_START_PRESS:lambda _: print("START_PRESS"),
pygame_gui.UI_BUTTON_PRESSED:lambda _: print("PRESSED"),
pygame_gui.UI_BUTTON_DOUBLE_CLICKED:lambda _: print("DOUBLE_CLICKED")}
command_button = UIButton((350, 280), 'Command', command=command_dict)

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (f1a433e) 95.83% compared to head (d0b8c98) 95.71%.
Report is 12 commits behind head on main.

Files	Patch %	Lines
pygame_gui/elements/ui_button.py	94.28%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #508      +/-   ##
==========================================
- Coverage   95.83%   95.71%   -0.13%     
==========================================
  Files          83       84       +1     
  Lines       11605    11676      +71     
==========================================
+ Hits        11122    11176      +54     
- Misses        483      500      +17     

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[MyreMylar]

This looks pretty good! It passes the existing testing (and adds some new tests) so we won't break anyone's code. I had a few ideas for making it a bit easier to use and clarify the documentation. Should be a familiar API to people coming across from tkinter which has a similar way of responding to button presses.

I think this could be expanded to hover events too without many changes but no need to do everything in one PR. I think PRs are often better kept focused as it makes them easier to review and judge their impacts.

[MyreMylar]

OK! Looks good to me.