Optionally disable the # value = ... in Printer

[dagardner-nv]

I'm running into an issue where pybind11-stubgen is appending # value = ... in stub files.
Similar to issue #222, the sub output includes values which change on every build, specifically repr's for PyCapsule objects:

attr : dict  # value = {'key': <capsule object "PyObject *(InfoData, PyObject *)" at 0x7f495e2efba0>}

I tried specifying --print-safe-value-reprs to avoid the this particular attribute however it doesn't appear to be invoked in this case.

In my case the attribute in question is private and the name is prefixed with __, an alternative for my use-case would be a flag to exclude names beginning with __.