More work needed on multipart parser

[andrew-d]

Multipart parser currently doesn't respect max-size limits. This needs to be done.

Also need more tests for the request body parser. Off the top of my head:

• Base64/quoted-printable/etc. encoding end-to-end
• Invalid line endings
• Fuzz testing so we don't end up in a strange state
• LOTS of unicode tests (filenames, field names, etc.)
• Upload two files with the same name, see what happens.
• Max-size support

[andrew-d]

With #4, more tests have been added. There's a TODO in the code to add more.