Add "until:" config setting

[jwodder]

Closes #75.

[codecov-commenter]

Codecov Report

Merging #76 (53752f3) into master (0215fbb) will decrease coverage by 63.50%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #76       +/-   ##
==========================================
- Coverage   67.31%   3.80%   -63.51%     
==========================================
  Files           9       8        -1     
  Lines         722     735       +13     
  Branches      100     107        +7     
==========================================
- Hits          486      28      -458     
- Misses        194     707      +513     
+ Partials       42       0       -42     

Impacted Files	Coverage Δ
src/tinuous/__main__.py	0.00% <0.00%> (-48.47%)	⬇️
src/tinuous/appveyor.py	0.00% <0.00%> (-82.67%)	⬇️
src/tinuous/base.py	0.00% <0.00%> (-93.11%)	⬇️
src/tinuous/config.py	0.00% <0.00%> (-90.79%)	⬇️
src/tinuous/github.py	0.00% <0.00%> (-51.29%)	⬇️
src/tinuous/travis.py	0.00% <0.00%> (-67.97%)	⬇️
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0215fbb...53752f3. Read the comment docs.

[yarikoptic]

Great, thank you @jwodder !