Add recipe for calver and trove-classifiers

[xylar]

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[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I wanted to let you know that I linted all conda-recipes in your PR (recipes/calver, recipes/trove-classifiers) and found some lint.

Here's what I've got...

For recipes/trove-classifiers:

• noarch: python recipes are required to have a lower bound on the python version. Typically this means putting python >=3.6 in both host and run but you should check upstream for the package's Python compatibility.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/calver, recipes/trove-classifiers) and found it was in an excellent condition.

[xylar]

@conda-forge/help-python, while OSX and Win tests are still running, I believe Linux test having passed indicate that this is ready for review.

[xylar]

@hmaarrfk, thank you!