Change new() to bless_code().

new() was very confusing because it didn't make a new object, it
blessed an existing code ref.  This meant there was weird code
where you didn't use the instance returned from new().

Avoid implying the new() paradigm and make a method which better
says what it does.

Also removed stash(), it was never used.
Merge pull request #4 from exodist/issue/1

Change new() to bless_code().