created a new generator-backed trading environment for testing.
other details:
    - also fixed grammatical errors in loader's status messages.
    - converting the treasury curves to an ordered dict.
    - moved to using a lambda for clarity as per @ehebert
    - initializing calendar end dates to be midnight of current date in
    - US/Eastern. Yahoo data isn't available until midnight eastern.
Merge pull request #90 from quantopian/fake_environment

Fake environment