Stop moving Juneteenth to Friday if Saturday for US-Fed calendar

[gbfredrik]

Hi,
These two links suggest the moving of Juneteenth to Fridays is incorrect for the Federal Reserve implementation:

• https://www.federalreserve.gov/aboutthefed/k8.htm
• https://www.frbservices.org/about/holiday-schedules

This currently leads to issues during 2027, 2032, etc. I've added a boolean to isJuneteenth to preserve the behavior for other calendar implementations.

[coveralls]

coverage: 72.136% (+0.02%) from 72.112%
when pulling 9160717 on Model-Validation:juneteenth-fed
into 5611dec on lballabio:master.

[lballabio]

Thanks! May you add the links to the docs in the header file?

[gbfredrik]

Thanks! May you add the links to the docs in the header file?

Done!