Use pyresample's boundary classes

[mraspaud]

Switch to pyresample's boundary objects instead of pytroll-schedule's

• Tests passed
• Passes git diff origin/develop **/*py | flake8 --diff

[coveralls]

Coverage decreased (-0.005%) to 65.515% when pulling 8afed92 on feature-pyresample-boundary into fe37d89 on develop.

[codecov]

Codecov Report

Merging #292 into develop will decrease coverage by 0.73%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #292      +/-   ##
===========================================
- Coverage    65.52%   64.78%   -0.74%     
===========================================
  Files          117      117              
  Lines        14275    14532     +257     
===========================================
+ Hits          9353     9414      +61     
- Misses        4922     5118     +196

Impacted Files	Coverage Δ
satpy/readers/utils.py	66.23% <100%> (+1.29%)	⬆️
satpy/readers/yaml_reader.py	84.64% <100%> (-0.46%)	⬇️
satpy/tests/test_yaml_reader.py	98.6% <100%> (-0.05%)	⬇️
satpy/readers/nc_nwcsaf.py	16.17% <0%> (-0.85%)	⬇️
satpy/composites/__init__.py	32.25% <0%> (-0.63%)	⬇️

---

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 fe37d89...8afed92. Read the comment docs.

[mraspaud]

I can't reproduce the error locally, so I'm going to test things out here. I'll do a squash merge in the end.