Move alias prefix into method class

This commit moves the alias prefix and adds #alias to the method class.
This simplifies using a methods alias since it is now generated on a
method.
Fix defining callbacks after the method definition

This commit fixes defining callbacks after the method definition. Since
the only time #redefine_method is hit is in the #method_added hook, if a
callback was defined after the method definition the method would never
get redefined. This commit adds a call to #redefine_method in #find_or_new
so that when a callback is defined we'll check if the method has been
defined yet, and if so, redefine the method.

This commit also adds conditions to #redefine_method to short circuit if
the method hasn't been defined yet or if we've already redefined the
method by checking if the method's alias has been defined.
Bump to version 1.1.0 and add CHANGELOG

This commit bumps the version to 1.1.0 and adds a CHANGELOG.