0.7.1 – String iterators

This release introduces string iterators into the API.

• String.bytes/0 - iterates over individual bytes in a string (yields Number)
• String.chars/0 - iterates over Unicode codepoints in a string (yields String)
• String.code_points/0 - same as String.chars/0, but yields Number
• String.lines/0 - iterates over LF or CRLF separated lines in the string (yields String)
• String.split/1 - splits the string into substrings using a separator, going from the left (yields String)
• String.rsplit/1 - splits the string into substrings using a separator, going from the right (yields String)