[whatwg] plaintext submission

[fantasai]

http://whatwg.org/specs/web-forms/current-work/#text-plain

I think this format is braindead, so I'm half-seriously proposing
a text/x-plain enctype to do something a little more sensible.

text/x-plain is handled exactly the same as text/plain except
step 4,

# 4. The control names/values are listed in the order they appear in the
# form data set. The name is separated from the value by `=' and
# name/value pairs are separated from each other by a newline character.

is replaced with

   4. Values are formatted by prepending a tab character and then inserting
      a tab character after every occurance of a newline in the value.

   5. The control names/values are listed in the order they appear in the
      form data set. Each name is followed by ' = ', then a newline, then
      the tab-indented value, and finally two more newlines.

      Multiple values for the same control are separated by a newline
      followed by two dashes followed by another newline.

~fantasai