Rewrite the protocol handling for better performances characteristics.

The qmynd wire-protocol implementation was eagerly loading up the whole
content of a MySQL packet as a sequence of unsigned-bytes in memory, only to
then read from a stream built on-top of that sequence.

The new wire-packet implementation is a transparent stream where the next
packet's chunk is crossed transparently from within read-my-byte and
read-my-sequence calls, resulting in only fetching the data we need at any
time and bypassing all the stream to sequence of bytes to stream again in
the parsing of the data.

In passing, we also fix the handling of data as text.

Tests ran against this code show it about twice as fast as the previous
coding in best cases, and when disabling compression. There's now an option
to disable it at connection time (default to disable), because it's
unexpected to see compression offering any gain on a "local" connection
anyway, even more when using salza and chipz.