Initialize all fields of zero token before returning it.
Merge pull request #14 from Shopify/init-zero-token

Initialize all fields of zero token before returning it.
Use C strict parser externally
Merge pull request #15 from Shopify/expression-parsing

Use C strict parser externally
Ensure Expression.parse matched the entire markup
Backtrack number cursor even at end of string
Sanity check token val/val_end
Merge pull request #17 from Shopify/ensure-markup-ended

Ensure Expression.parse matched the entire markup
WIP block parsing
Update for BlockBody
Various cleanup
Further cleanup and review comments