implement parseLiteralExpr for object/array literals including nesting and bare-identifiers
rewrite parseLiteralExpr to handle variables (not inside object/array literals)
refactor parseExpr based on parseLiteralExpr; get all tests passing with new code
fix token regex from breaking on: {% set foo = { bar: "bar" } %}
rewrite filter args and for/in parsing
fix bug in parseFilter
bump version to 0.1.3; update docs