Update workalendar to 2.6.0

[pyup-bot]

This PR updates workalendar from 2.3.1 to 2.6.0.

Changelog

2.6.0

New Calendars

- Added Angola, by dvdmgl (276)

Bugfixes

- Portugal - removed carnival from Portuguese holidays, restored missing holidays (275)

Other changes

- Added All Souls Day to common (274)
- Allow the `add_working_days()` function to be provided a datetime, and returning a `date` (270).
- Added a `keep_datetime` option to keep the original type of the input argument for both ``add_working_days()`` and ``sub_working_days()`` functions (270).
- Fixed usage examples of ``get_first_weekday_after()`` docstring + in code (calendars and tests) ; do not use magic values, use MON, TUE, etc (271).
- Turned Changelog into a Markdown file (272).
- Added basic usage documentation, hosted by Github pages.
- Added advanced usage documentation.

2.5.0

- Bugfix: deduplicate South Africa holidays that were emitted as duplicates (265).
- Add the `get_working_days_delta` method to the core calendar class (260).

2.4.0

New Calendars

- Added Lithuania, by landler (254).
- Added Russia, by vanadium23 (259).

Bugfixes

- Fixed shifting ANZAC day for Australia states (249).
- Renamed Australian state classes to actual state names(eg. AustraliaNewSouthWales to NewSouthWales).
- Update ACT holidays (251).
- Fixing Federal Christmas Shift ; added a `include_veterans_day` flag to enable/disable Veteran's day on specific calendar - e.g. Mozilla's dedicated calendar (242).

Other

- **Deprecation:** Dropped support for Python 3.3 (245).
- Fixed Travis-ci configuration for Python 3.5 and al (252).
- Moved from `novafloss` to the `peopledoc` organization, the core People Doc Inc. organization (255).
- First step iteration on the "global registry" feature. European countries are now part of a registry loaded in the ``workalenda.registry`` module. Please use with care at the moment (248).
- Refactored Australia family and community day calculation (244).

Links

• PyPI: https://pypi.org/project/workalendar
• Changelog: https://pyup.io/changelogs/workalendar/
• Repo: https://github.com/peopledoc/workalendar

[pyup-bot]

Closing this in favor of #68