Allow Macro.escape([1|2])

This fixes #1646
Merge pull request #1648 from pminten/quote-improper-lists

Allow Macro.escape([1|2])
Allow any function identifier as a variable, closes #1649
Remove empty Tuple module
Add Enum.slice/3
Merge pull request #1650 from ericmj/enum-slice

Add Enum.slice/3
Update CHANGELOG
Add a count guard check for slice