DOC: fix wrong copy-paste in the rspdel example

As reported by Cristian Ditoiu, the rspdel example is based on the reqrep
action, which is quite confusing!
DOC: readme: add suggestion to link against static openssl

Adds a suggestion in README howto link against a static build of openssl.

This is useful if the OS includes an old openssl releas and recent features
or ciphers are required.
MINOR: counters: make it easier to extend the amount of tracked counters

By properly affecting the flags and values, it becomes easier to add
more tracked counters, for example for experimentation. It also slightly
reduces the code and the number of tests. No counters were added with
this patch.
MEDIUM: counters: add support for tracking a third counter

We're often missin a third counter to track base, src and base+src at
the same time. Here we introduce track_sc3 to have this third counter.
It would be wise not to add much more counters because that slightly
increases the session size and processing time though the real issue
is more the declaration of the keywords in the code and in the doc.
MEDIUM: counters: add a new "gpc0_rate" counter in stick-tables

This counter is special in that instead of reporting the gpc0 cumulative
count, it returns its increase rate over the configured period.
BUG: ssl: send payload gets corrupted if tune.ssl.maxrecord is used

We were using "tune.ssl.maxrecord 2000" and discovered an interesting
problem: SSL data sent from the server to the client showed occasional
corruption of the payload data.

The root cause was:
When ssl_max_record is smaller than the requested send amount
the ring buffer wrapping wasn't properly adjusting the
number of bytes to send.

I solved this by selecting the initial size based on the number
of output bytes that can be sent without splitting _before_ checking
against ssl_max_record.
BUG: ssl: fix crt-list for clients not supporting SNI

I left a mistake in my previous patch bringing the crt-list feature,
it breaks clients with no SNI support.

Also remove the useless wildp = NULL as per a previous discussion.