Added GitHub action to do axe accessibility tests with [axe
cli](https://github.com/dequelabs/axe-core-npm/tree/develop/packages/cli).
I believe it is best by default to let this be run only manually, since
fixing some of the issues are not straightforward (I haven't fixed them
all for this template yet).
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Signed-off-by: George Araújo <george.gcac@gmail.com>
summary:
- adds prettier formatter configuration
- formats the entire repo using prettier, ignoring minified files
(`*.min.css`) and heavy generated html
- changes extensions of all `.html` files to `.liquid`, which is more
correct and necessary for prettier to work correctly
- replaces "%-" and "-%" with just "%" — manual liquid formatting using
minus signs is superfluous since we are compressing and minifying the
code anyway
- adds CI action for running prettier check on PR and pushes to master
George
Maruan