Add Carbon Period functionality (#78)

* Add Carbon Period functionality

* Add unit tests that check errors in carbon period

[RFC] Fix month calculation between dates (#77)

* Fix month calculation between dates

* Remove unused function

[RFC] Fix language, use go:embed (#76)

* Fix language, use go:embed

* Update readme with new badge

* Set badge name to Build Status

[RFC] Fix incorrect diff in months (#74)

* Fix incorrect diff in months

* Improve naming of test

Remove unused variable secondsInMonth (#53)

Fix SetTimestamp in the correct location (#50)

* Add Test SetUnix

* SetTimestamp in the correct location

Fix SetTimestamp in the correct location (#50)

* Add Test SetUnix

* SetTimestamp in the correct location

[RFC] Add diffInMonths fix for NonUTC zones (#49)

* Add diffInMonths fix for NonUTC zones

* Add test to reproduce issue (#46)

* Copy the instance

* Remove duplicated test

Add CreateFromMonthAndYear (#44)

[RFC][UN-13487] Fix diff in months (#43)

* Fix diff in months counting months twice

* Add carbon php tests

* Fix logic all test suite passes

* Add negative date tests

* Refactor diff in months