Improvements to `Entry`

[eschan145]

Multiple improvements can be added to the Entry.

• Capitalize all instances of "Entry" in README.md
• Adding select-all with Control—A
• Adding clipboard enhancements with Control—C and Control—V
• Adding rich text formatting to Entry
• Adding option to make Entry multiline
• Caret not showing up in line start
• Caret invisible or visible instead of changing color when blinking
• Caret glitching on blinks at line end
• Undo and redo features
• Enable updates for smoother updates. This raises an AssertionError, one that has been seen before.
• Show feature for passwords