parse_form_data(
boundary,body) ->args
Parse a multipart/form-data body into a key-value table
Parses a multipart/form-data body using the given boundary string, as the request's Content-Type carries it, unquoted. The boundary is matched as plain text. Each part's headers are read by name, in any case and in any order, up to the first blank line.
A text field comes back as its bytes as sent: no decoding, no escaping.
The caller escapes one at output. A part with a non-empty filename
comes back as a table with filename, content, and content_type,
the part's Content-Type as sent, or nil when the part has none. An empty
filename, which a browser sends for an empty file input, makes a text
field. A part with no name is skipped, and a later part replaces an
earlier one of the same name.