Refactor BrazilBankCalendar to use include_* flags

[iurisilvio]

It is really useful to allow reuse of this class. Brazilian bank calendar is not always the same.

For my use case, I just want to remove ash wednesday, but for that I have to override get_variable_days().

• Tests with a significant number of years to be tested for your calendar.
• Changelog amended with a mention describing your changes. Note Please do NOT change the version number here. It's the project maintainers' duty.

Related #474

[brunobord]

Thank you very much for this very valuable change, it makes much more sense now.
To be honest, I think we could also remove the redefinition of Christmas Day. In every Christian calendar, Christmas Day is a holiday, so I wonder why it was added in the first place.

Do you think you could add this small patch to your PR, please? (otherwise I may give it a go later on)

[iurisilvio]

Done! Removed Christmas Day.

[brunobord]

a bit overwhelmed at the moment, but I'm going to merge this and make a bugfix release as soon as I can. thank you again a bunch for this patch, I love it!