Interval with independent endpoint types

[zsunberg]

See #121 for conceptual discussion.

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.12%. Comparing base (fade689) to head (7eae506).
⚠️ Report is 58 commits behind head on master.

Files with missing lines	Patch %	Lines
src/interval.jl	94.44%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (fade689) and HEAD (7eae506). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (fade689)	HEAD (7eae506)
	12	4

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #122       +/-   ##
===========================================
- Coverage   99.13%   89.12%   -10.02%     
===========================================
  Files           3        3               
  Lines         232      239        +7     
===========================================
- Hits          230      213       -17     
- Misses          2       26       +24     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.