Semiprime 4.x issue518

[niccokunzmann]

This is a continuation of #524, fixing the CI tests.

• merges 4.x branch: Fix for issue 518 (to_ical() with RRULE BYDAY values>=10) #524
• contributes to RRULE BYDAY=xMO with x >=10 raises ValueError with to_ical() #518
• contributes to the 4.x branch
• makes CI run on 4.x again
• adds auto deploy to 4.x from tags
• removes testing 2.7 (still covered by pypy2)
• removes testing 3.4 (runners for ubuntu 18 are not available)
• adds documentation about the two deprecated tests to the README

[coveralls]

Pull Request Test Coverage Report for Build 6021342796

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 90.758%

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Totals
Change from base Build 2985568065:	0.2%
Covered Lines:	1149
Relevant Lines:	1266

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 6021605870

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 90.758%

---

Totals
Change from base Build 2985568065:	0.2%
Covered Lines:	1149
Relevant Lines:	1266

---

💛 - Coveralls

[niccokunzmann]

This PR is also ready for review, you are invited :)

[niccokunzmann]

Merging this to try out a new 4.x release.