String Additions

String capitalization. Index-based insertion, replacement, and removal. Similar implementation of C# String.Format(..) to allow for terse index-based string interpolation without needing to use a literal with '$var' at the time of interpolation.
Really nitpicky style comment: generally avoid "allows you to" in favour of more precise language. I realize that `loop` is documented that way, but we were naughty. ;)