docgen: allow excluding emitting docs for 3rd party libraries

[AtomicSynth]

Currently it's possible to exclude emitting only the docs for the stdlib, but I think it would be great to omit 3rd party dependencies as well as that documentation may be irrelevant to the current package + the user may not end up using the 3rd party library of a package.

I currently have project Volt, that depens on Ion. User may never end up using Ion at all and may be interested in Volt as I distribute docs.html in my c3ls.

[ManuLinares]

I'll write an example here that excludes the std::atomic or the std::atomic::types modules

TEMPLATE="${TEMPLATE:-resources/docs.html}"

{
  sed '/\/\*DATA_START\*\//q' "$TEMPLATE"

  printf '\n\t\tEMBEDDED_JSON_LIST.push({ target: "default", data: '

  c3c docgen lib/std/ --json |
  jq 'del(
    .modules["std::atomic"],
    .modules["std::atomic::types"]
  )'

  printf '});\n'

  sed -n '/\/\*DATA_END\*\//,$p' "$TEMPLATE"
} > mydocs.html

This is just to demonstrate how this can be achieved with the c3c docgen --json output, and for future reference for when/if this filter feature gets implemented.