ASCompletion: rewrote "Add Closing Braces", closes #357
Fix closing braces in string interpolation expressions
Support {} braces, don't duplicate closing braces when there already is one
Fix indent on newline on while in {}-braces caused by smart-indent, some cleanup
Update docs of  "Add Closing Braces"
Merge pull request #369 from Gama11/AddClosingBraceRefactor

Rewrote "Add closing braces", closes #357