Push API for parser

[fmayer]

Hey! currently there are three APIs to parse:

• load_from_string
• load_from_iter
• load_from_parser

AFAICT all of those are "pull" style, as in you supply the input, and the parser requests them. Sometimes, e.g. when reading from the network or a file, it would be easier to supply data to the parser as you have it, and then signal you are done to finalize.

[MihaMarkic]

Could you create an iterator over reading from file (stream) and use it with load_from_iter?