Deprecate 'enhancement_config' keyword argument in favor of 'enhance'

[djhoese]

Current ways of specifying custom enhancement are inconsistent between save_dataset-type methods and get_enhanced_image and the Enhancer class that actually applies the enhancement. There is enhancement_config and enhancement_config_file, but most of the time the user just wants to say "don't enhance anything". To me the clearest way that a user could ask for this would be:

scn.save_dataset(..., enhance=False)

which is now how it works. A user can also provide a Enhancer instance if they really want to. This PR also sets things up for the future where I would like to reinvent the enhancement interface to make it a separate step for the user.

• Tests added
• Tests passed
• Passes git diff origin/master -- "*py" | flake8 --diff
• Fully documented

[coveralls]

Coverage increased (+0.007%) to 73.939% when pulling 2b335e4 on djhoese:feature-enhance-kwargs into 5dd28ea on pytroll:master.

[codecov]

Codecov Report

Merging #485 into master will increase coverage by <.01%.
The diff coverage is 93.61%.

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
+ Coverage   73.93%   73.93%   +<.01%     
==========================================
  Files         137      137              
  Lines       18222    18242      +20     
==========================================
+ Hits        13472    13488      +16     
- Misses       4750     4754       +4

Impacted Files	Coverage Δ
satpy/tests/writer_tests/test_mitiff.py	95.12% <ø> (-0.06%)	⬇️
satpy/tests/test_scene.py	99.32% <ø> (-0.01%)	⬇️
satpy/scene.py	84.03% <100%> (-0.43%)	⬇️
satpy/writers/geotiff.py	43.51% <100%> (ø)	⬆️
satpy/writers/mitiff.py	74.86% <100%> (ø)	⬆️
satpy/tests/test_writers.py	97.31% <100%> (+0.11%)	⬆️
satpy/writers/scmi.py	74% <100%> (ø)	⬆️
satpy/writers/__init__.py	76.19% <87.5%> (+0.16%)	⬆️

---

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 5dd28ea...2b335e4. Read the comment docs.