Omit endpoint parameters marked with x-hidden

[brotheroftux]

Main changes:

• Endpoint parameters marked with x-hidden are now filtered out before rendering
• Parameter groups (query, path, cookie, etc.) are now omitted if all of their respective params are marked as hidden

Additional comments:

• We did not previously have tests for hidden props on object schemas — I added a test suite. I also believe it is possible to have an empty table rendered for a component if all of its properties are marked as hidden, but I didn't fix this behaviour yet.