Extra features: Improved/Added commands to match Github, Added line/lines duplication/movement

[RARgames]

Hey @jaywcjlove, I've added a few features to your editor (that I needed):

• Enhanced ALL default command buttons (e.g. bold, italic, list) to match Github behavior (e.g. include remove feature)
• Added table, mention, issue, help commands
• Added Ctrl+D to duplicate line/lines
• Added Alt+UpArrow/DownArrow to move line/lines

Feel free to include some/all of them in your project if you think that features are useful. (I can start a PR if you want. Repo is available here. Code is tested and everything should work, some command tests are missing e.g. remove feature.)

To anyone else interested: Feel free to use it, if you need these features.

[jaywcjlove]

@RARgames Welcome to submit PR

There are currently too many maintenance items. So if you are interested, you are welcome to submit a PR.

[RARgames]

Created #580