Minor edits to introduction

While it might be interesting for librdkafka developers
to see the difference between in-queue and in-flight timeouts
this change also changed the expected error returns from delivery reports, et.al.,
and thus was a badly documented API:ish change.

This commit reverts back to the previous functionality with emitting TIMED_OUT
for in-queue timeouts.

add weiboad/aidp project links

Builtin SASL PLAIN and SCRAM support

It is easier to maintain and test just one implementation.

The timeout was wrongfully set to 1 second instead of 10.
Additionally we no longer set an explicit timeout (use socket.timeout.ms instead)
if api.version.request is enabled.

Fixes memory leak from Base64 decoder

Supports SCRAM-SHA-1, SCRAM-SHA-256 and SCRAM-SHA-512
Do note that SCRAM-SHA-1 is not currently supported by broker 0.10.2.0

Add TLS SNI (serve name) when connecting with SSL. If the broker is
behind a load balancer, the load balancer can use this information to
locate the right server.