Check that tidy supports the mute option (#345)
Check that tidy supports the mute option (#345)

macOS comes with tidy but it is an old version that does not support the
`--mute` option. This leads to spurious test failures on macOS.

This adds a check to is_present_in_path that requires the available
version of tidy support the mute configuration option before it will be
used.
ocaml-doc/odoc,ocaml-doc/odoc