Refactor Lexer::Character to be a SimpleDelegator of String

[fractaledmind]

As I first built it, Feather::Lexer::Character is an independent class that accepts a single string character. I manually delegate the #ord method, but it should more generally decorate the String instance. SimpleDelegator is a straightforward way from the Ruby standard lib to implement decorators. We should make Feather::Lexer::Character a SimpleDelegator of String.