maintenance PR

[sappelhoff]

I'll finish this piece by piece

• add conda-forge badge and conda install instructions
• update BrainVision Core Data Format specification (the spec to which this code should adhere)
• move from circleCI to github actions (testing on win, macos, linux instead of only linux)
• test for different mne and python versions
• get coverage to 100%
• test the read example we advertise in the README

Also I wrote to readthedocs to please enable Pull Request Build Artifacts for us ... this will replace the circleci artifact. (for a preview to how it looks, see the "checks" section in this PR)

[codecov]

Codecov Report

Merging #43 into master will increase coverage by 4.66%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master       #43      +/-   ##
===========================================
+ Coverage   95.33%   100.00%   +4.66%     
===========================================
  Files           3         3              
  Lines         236       254      +18     
===========================================
+ Hits          225       254      +29     
+ Misses         11         0      -11     

Impacted Files	Coverage Δ
pybv/__init__.py	100.00% <100.00%> (ø)
pybv/io.py	100.00% <100.00%> (+7.09%)	⬆️
pybv/tests/test_bv_writer.py	100.00% <100.00%> (ø)

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[sappelhoff]

got a reply from Readthedocs, so testing whether this works now :)

Hi Stefan!
I've just enabled the feature for you, you should be able to enabled the pull request builds now.
You can find our docs on this feature here: https://docs.readthedocs.io/en/latest/guides/autobuild-docs-for-pull-requests.html, let us know if you have any more questions or have any feedback!
Regards,
Anthony