Merge branch 'master' of https://github.com/quantopian/zipline

* 'master' of https://github.com/quantopian/zipline:
  MAINT: Use more exact boolean checks for pandas structures.
  BUG: Fix typo in requirements file.
  BLD: Add mock to requirements file.
  BLD: Update to latest tornado release.
  BLD: Update to latest Cython release.
  ENH: Add Brazilian calendar for BMF&Bovespa stock market
  ENH: Factor out API methods. Add support for algo scripts.
ENH:Working version of tradingcalendar as a class