This commit adds initial support for international markets in the Pipeline API
via addition of the concept of "domains".
Significant changes on this branch include:
- Added `zipline.pipeline.domain` and the `Domain` interface.
- Added several canonical domain definitions:
- GENERIC
- US_EQUITIES
- CA_EQUITIES
- GB_EQUITIES
- Added `zipline.country` as a place to define canonical country code names.
- Made `PipelineLoader` an interface and added new `domain` parameter to
signature of `load_adjusted_array`.
- Added a new system for "generic" and "specialized" DataSet and BoundColumn
objects.
- Added a new system for inferring a domain from a pipeline that contains a mix
of generic and non-generic terms.
- Reworked the built-in pricing dataset. USEquityPricing dataset is now a
specialized version of a generic EquityPricing dataset, and most built-in
factors are now implemented in terms of EquityPricing rather than
USEquityPricing.
- Removed `zipline.data.us_equity_pricing`.
- Moved BcolzDailyBar{Reader,Writer} to `zipline.data.bcolz_daily_bars`.
- Moved SQLiteAdjustment{Reader,Writer} to `zipline.data.adjustments`.
New dependencies added as part of this work:
- iso3166 (for canonical country code definitions)
- python-interface (for strict interface definitions).
See https://github.com/quantopian/zipline/issues/2265 for a full description of
the design for domains.
