Changed dependency from mockito-all to mockito-core.

Mockito-all depends on hamcrest 1.1, but JUnit depends on hamcrest 1.3.
This difference causes tests to throw NoSuchMethodError, due to a
newly introduced describeMismatch() method in hamcrest's Matcher class.
Fixed the bug where USD holiday between T and T+1 is not ignored.
Added licensing.
Added README.md.
Inlined expectations.

Reduces clutter and makes the assertions clearer.
Implemented handling of weekends when computing spot date.
Added missing license header to CurrencyHolidays source.