pdf_dict, array, stream has/get/get_mut

[burrbull]

split
pdf_lookup_dict() on .as_dict().has(), .as_dict().get() and .as_dict().get_mut()
pdf_get_array on .as_array().get() and .as_array().get_mut()
stream_dict on .as_stream().get_dict() and .as_stream().get_dict_mut()

use output_xref: Vec<xref_entry>

[crlf0710]

While this seems good, why don't you just change these into methods...

[cormacrelf]

@crlf0710 they are methods on pdf_obj in #176, but practically nowhere in the code is there a rust reference, only raw mut pointers, so they are difficult to call at the moment.

[burrbull]

Ok. I'll try.

[crlf0710]

Seems good, merging~