after_date can accept multiple values now

[semaphoreP]

Addressing #335, the after_date keyword in basis.tau_to_tp can now accept numpy arrays. Test included to check it works.

[coveralls]

Pull Request Test Coverage Report for Build 5395991210

• 4 of 4 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 86.431%

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Totals
Change from base Build 5357401207:	0.007%
Covered Lines:	5153
Relevant Lines:	5962

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💛 - Coveralls