Allow indentation with spaces

[WebCoder49]

This should allow the indent plugin to take in an optional number-of-spaces parameter; setting it to 0 or not setting it (for backwards compatibility) should use tabs. This seems important because both CodePen and VS Code use spaces as indentation, as well as the Google JS Style Guide, etc. Functionality involves:

• Making tab key presses generate correct numbers of spaces
• Make the enter key processor use these space indentations
• Make the backspace key presses delete whole indentations at once

Please give a thumbs up below if you agree this should be an option or comment if you have any suggestions / questions.