Basic math and calendar system implementation and tests
Minor rearrangements
Gregorian Date implementation refactoring
More tests for Month data type
More tests for Month
gregorianDate function should use gregorian chronology implementation to
get fixed date value.
organize impoerts
Fixed a bug in a month computation
additional unit tests
refactor from Roland Tepp continued
Merge remote-tracking branch 'RolandTepp/M5/calcalc' into
M5/calcalc_gregorian_date

Conflicts:
	tests/test/ceylon/time/dates.ceylon
Merge pull request #15 from DiegoCoronel/M5/calcalc_gregorian_date

Implementation of Gregorian calendar chronology based on the algorithms introduced in Calendrical Calculations book