Fix warning for unused default arguments
Make String.slice consistent with Ruby semantics, closes #1034
Merge pull request #1076 from mururu/default_args

Fix warning for unused default arguments
Merge pull request #1077 from meh/string-slice

Make String.slice consistent with Ruby semantics, closes #1034
Change == to === in tests for String.to_integer and String.to_float.
Merge pull request #1079 from jdeisenberg/string_to_int_float

Change == to === in tests for String.to_integer and String.to_float.
Remove if in favor of extra function clause
Also convert String.to_integer tests to use ===
Add Enum.at/2, Enum.at/3 and Enum.fetch/2