Improvements to the Entry widget

[eschan145]

Multiple improvements can be added to the Entry widget.

Improvement	Type	Details	Progress
Select all text with Control—A	Enhancement	Common in most text input fields	✅
Adding clipboard modification	Enhancement	Should use Control—C, Control—X and Control—V. Currently works but has to use tkinter. Pyglet does track these Copy and Paste events, but is unable to handle them. See a related GitHub issue for details.	⚒️
Rich text formatting to entry	Enhancement	Go to GitHub issue	⚒️
Option to make entry multiline	Enhancement	Needs to have correct sizing beforehand. Stack Overflow question	⚒️
Undo and redo features	Enhancement
Caret not showing up on line start	Bug	Only occurs before any text is typed, and with a blank entry. Pyglet-related problem. May be fixed in the near future or on an upcoming release.	❌
Caret invisible or visible instead of changing color when blinking	Bug	Fixed by modifying pyglet rendering	✅
Caret glitching on blinks at line end	Bug	Pyglet-related problem. May be fixed in the near future or on an upcoming release	❌
Using speedups for glyph recalculation	Enhancement	Use pyglet.text.layout.TextLayout.begin_update() and pyglet.text.layout.TextLayout.end_update() for saving recalculation of glyphs and speeding updates. This sometimes raises an AssertionError, one that has been seen before.	⚒️
Show feature for passwords	Enhancement	See tkinter's -show option for its Entry widget.	⚒️