working on it
Merge branch 'next' into 2048_v2
Revert "Revert "Made slice's second argument optional.""

This reverts commit 214e094ea5710efe517dccdf10ec58ca38ecc457.
undid changes to ast.py
making second parameter to slice optional for js and py; updating polyglots
Merge branch 'grey_issue_2048' into next