I came for something else, but one thing led to another...

Emit a proper summary at the top, but elide ENUMs to keep it
compact.

If the entire VCL prototype fits in the header, put it there.
else if it fits with ENUMs elided do that or finally resort
to just the name + "(...)".

If the header didn't hold the full prototype, emit a codeblock
with it, and split that in one line per argument if it is too
wide for the manual pages.

Remove the manual summary from the libvmod_blob docs.

otherwise summarize it (ie: elide ENUMs)

And sync bin/varnishd/Makefile.am to use the same (and more accurate)
variable name.

Spotted by Reza.

generated VCL synopsis:

old:	new OBJ = VOID dyn(STRING addr, STRING port)
new:	new OBJ = dyn(STRING addr, STRING port)

Spotted by:	simon

Ref: aa8875a4
Ref: c310f04b

Fixes 2461

Fixes #2386

I don't think it matters anywhere else, but future-proofing is good.

Hopefully fixes #2586

This should help readability of the code, hopefully.

The API remains unchanged.

Local variables for vsl_status are called 'r', variables holding
a VSLQ_dispatch_f return value are called 'i'

Makes it possible to distinguish listeners in a VSL client
transaction. Especially if there is more than one UDS listen
address, since all of them are logged as the bogo-IP 0.0.0.0:0
where addresses are logged.

pipe remains the only exception.

Ref: https://tools.ietf.org/html/rfc7230#section-2.6

   Intermediaries that process HTTP messages (i.e., all intermediaries
   other than those acting as tunnels) MUST send their own HTTP-version
   in forwarded messages.

Closes #2574

Avoid keeping H/2 streams alive indefinitely.

This adds timeouts for:
  - How long we allow a stream to wait for a WINDOW_UPDATE, subject
    to idle_send_timeout
  - Total duration after we started transmitting a response,
    subject to send_timeout

We currently do not make any attempt at sending a GOAWAY or a PING for
client inactivity. This may be something to reconsider at a later point.

In particular H2TxHdr, H2TxBody, H2RxHdr and H2RxBody will now be masked
out by default.

Document workaround for ESI (also works for gzipery).

Fixes #2554