Ansi-string

- Fixed concatenation
- Added operator: ==
- Added operator: in
- Added operator: len()
- Added center(), ljust(), rjust() justification methods
- Added lower() and upper() case methods
- Added lstrip(), rstrip(), and strip()
- Removed internal use of copy.deepcopy(), added copy()
- Simplified `__format__`: call center(), ljust(), rjust() justification methods instead of redefining & general refactoring

- Changed apply_formatting() to take start/end rather than start/length
- Added more string-like functionality (supports + and +=)
- Added tests