Import Existing Pax-Calendar work.

Pull existing Pax-Calendar work into threeten-extra repo branch.
Add contributor line to the .pom file.
Revert "Add contributor line to the .pom file."

This reverts commit 16845efb44757b78c94be1438e90289322b9797b.
Append contributor to file (this time taking into account line
terminators).
Delete unnecessary test classes
Move/Rename files to namespace directories.
Update package names.
Update/Add copyright blurb for project
Update to conform to existing package test names.
Update to conform to existing package test location.
Update to conform to existing package test implementation.
Update method names in TestPaxChronology.

Update method names in TestPaxChronology to conform to existing style.
Update method locations in TestPaxChronology

Update method locations in TestPaxChronology to conform to existing
examples.  (Also update a few overlooked method names.)
Update/Add data samples.
Update test_LocalDate_from_PaxDate signature.
Add range of tests using "samples" data.
Add data for bad dates.
Add test for bad dateYearDay
Add tests for leap year.
Add length of month (leap related)