Indexing of strings

Closes LOOP-197 LOOP-168 LOOP-169 LOOP-170 LOOP-171 LOOP-200 LOOP-196 LOOP-201

What has changed:

• Can now index strings the same as you can index arrays
  • Added tests too
• Can now slice strings and arrays by indexing: arr[0..4] or "hello"[1..3]
  • Added tests too
• Removed a whole bunch of unused code
• Added code owners
• Using result<> in compiler, instead of Compiler::Result
• Using ? token to catch errors in Picasso parser instead of manual checking
• Fixes the filepaths of multi level imports of Loop packages
• Documentation for instructions in Vinci