[REQS-712] Light-weight holiday source proposal
[REQS-712] Light-weight holiday source proposal

Per review, renaming class to use Store suffix, removing support for retrieving holidays per currency
[REQS-712] Using a set rather than a list for collection of holidays
[REQS-712] javadoc
[REQS-712] javadoc typo
[REQS-712] Changing the map key

Should allow isHoliday look-ups without creating a set
[REQS-712] Adding method to check from the map key directly
[REQS-712] Handling week-ends

Same behavior wrt weekends as MasterHolidaySource, i.e. isHoliday returns true if date falls on a Saturday or Sunday
[REQS-712] Returning a Set

Per review, in case one wants to use Set-specific methods
Merge pull request #278 from OpenGamma/topic/REQS-712

[REQS-712] Light-weight holiday source proposal