String functions

All of the string functions' parameters and return values are UTF-8 encoded strings. Any arguments or returned values to string functions which utilize offsets and lengths operate using code points.

`CaseFold`	Converts a string into a case-normalized string.
`Concat`	Combines a list of strings into a single string.
`FindStr`	Searches for a string within a string.
`FindStrRegex`	Searches for a regex pattern within a string.
`LTrim`	Removes all whitespace from the start of a string.
`Length`	Returns the length in codepoints of a string.
`LowerCase`	Converts a string to all lowercase.
`RTrim`	Removes all whitespace from the end of a string.
`Repeat`	Creates a new string by repeating a string multiple times.
`ReplaceStr`	Replaces a portion of a string with another string.
`ReplaceStrRegex`	Replaces a pattern in a string with another string.
`Space`	Creates a whitespace string of the specified size.
`SubString`	Returns a portion of a string.
`TitleCase`	Converts a string to use TitleCase.
`Trim`	Removes all whitespace from the start and end of a string.
`UpperCase`	Converts a string to all uppercase.