todo.txt

- parser:
    - observable pairs
        - all identifiers => observe scope with an identifier path
        - . operator => observe left-hand side on right-hand side path
        - [] operator => similar to . but what about arg ->
    - multiple scopes
    - undefined values for operators
    - bullet-prof error handling
    - optimisations
        - tree size:
            - drop the from info
            - operator names
            - objects => arrays
        - access time:
            - path access optimisation
            - constant folding
    - add index.js with entry points?
    - what about one-time binding => it sounds like a separate concern...
- multi-expression parser
    - make delimits configurable => it is not obvious in the CJS env :-/

- travis CI with FFox + Chrome + Sauce => make it work on IE8+