Add support for manipulating form

Being able to add, remove, and edit the fields in the form object would be nice.
I'm currently trying to scrape a website where there are 2 fields of the same name on the form and one of them needs to be deleted. Are there already methods for that?

Start by locating the form object and reviewing its existing field-handling API, then reproduce a form containing two fields with the same name. Done means the form supports adding, removing, and editing fields, including removing one selected duplicate field.

Written by the indexing model from the issue text.