If cowboy_static is initialized with `{priv_file, ...}` or `{priv_dir,
...}`, it is now able to read files from Erlang application .ez
archives.

When serving a file from an archive, the #file_info{} comes from the
archive, not the contained file, except for the size and type. The
erl_prim_loader module is used to read the latter's #file_info{} and the
actual file content (ie. sendfile(2) is not used in this case).

(cherry picked from commit 2166733628bbab0eb77eeed58bdf204727c48ec6)

Fixes #839 when 'Connection: Keep-Alive' wasn't sent in a HTTP/1.0
response. Now the usage of 'Connection' header is consistent with
current protocol version: when this header is not specified explicitly
in the response, HTTP/1.0 implies 'Connection: close' and HTTP/1.1
implies 'Connection: Keep-Alive'. So if current 'Connection' value
matches the default value of current protocol, we won't state obvious
fact in the response; and vice versa.

Amended to fix and improve tests, and revert the variable name
change from HTTP11Headers to StdHeaders. I think it's still good
to leave it as is because it's not really a standard header for
HTTP/1.0, and it's gone from HTTP/2 entirely.

Only go for keep-alive if they submit a 'connection: keep-alive' header
in the request, keep behaviour the same otherwise.

The new RFC 7230 (http://tools.ietf.org/html/rfc7230#section-6.3)
states:

    If the received protocol is HTTP/1.0, the "keep-alive" connection
    option is present, the recipient is not a proxy, and the recipient
    wishes to honor the HTTP/1.0 "keep-alive" mechanism, the
    connection will persist after the current response;

Even though clients are discouraged from doing so in Appendix A.1.2
(http://tools.ietf.org/html/rfc7230#appendix-A.1.2)

This is a first step to improve the HTTP status codes returned
by Cowboy on crashes. We will tweak it over time.

Also fixes a small bug where two replies may have been sent
when using loop handlers under rare conditions.

422 is undefined for HTTP and interpreted as 400.

The options were added to allow developers to fix timeout
issues when reading large bodies. It is also a cleaner and
easier to extend interface.

This commit deprecates the functions init_stream, stream_body
and skip_body which are no longer needed. They will be removed
in 1.0.

The body function can now take an additional argument that is a
list of options. The body_qs, part and part_body functions can
too and simply pass this argument down to the body call.

There are options for disabling the automatic continue reply,
setting a maximum length to be returned (soft limit), setting
the read length and read timeout, and setting the transfer and
content decode functions.

The return value of the body and body_qs have changed slightly.
The body function now works similarly to the part_body function,
in that it returns either an ok or a more tuple depending on
whether there is additional data to be read. The body_qs function
can return a badlength tuple if the body is too big. The default
size has been increased from 16KB to 64KB.

The default read length and timeout have been tweaked and vary
depending on the function called.

The body function will now adequately process chunked bodies,
which means that the body_qs function will too. But this means
that the behavior has changed slightly and your code should be
tested properly when updating your code.

The body and body_qs still accept a length as first argument
for compatibility purpose with older code. Note that this form
is deprecated and will be removed in 1.0. The part and part_body
function, being new and never having been in a release yet, have
this form completely removed in this commit.

Again, while most code should work as-is, you should make sure
that it actually does before pushing this to production.