support ClassVar,

[samuelcolvin]

Change Summary

exclude attributes annotated with ClassVar from fields

Related issue number

fix #184

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes
• No performance deterioration (if applicable)
• HISTORY.rst has been updated
  • if this is the first change since a release, please add a new section
  • include the issue number or this pull request number #<number>
  • if you're not a regular contributer please include your github username @whatever

[codecov]

Codecov Report

Merging #339 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #339   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          13     13           
  Lines        1805   1808    +3     
  Branches      352    353    +1     
=====================================
+ Hits         1805   1808    +3

[samuelcolvin]

I guess if we were perfect we'd add a section to documentation on this, but for now I can't be bothered.