bats pitch: Fix pitch_message_decode() API

This changes the pitch_message_decode() API to follow the same
convention as itch41_message_decode() which avoid a memcpy() in
libtrading internals.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
bats pitch: Add Symbol Clear message definition

Add Symbol Clear message definition. The PITCH specification says that
the message type was added on September 14, 2012 and been in effective
use since February 15, 2013.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
bats pitch: Add bats prefix to source files

Follow the same naming convention as other protocols and add bats prefix
to source files.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
bats pitch: Fix pitch_message_decode()

PITCH messages contain a 8 byte timestamp before message type.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
bats pitch: Make message type unsigned

It's easier to use ->MessageType in application code when you don't need
to worry about signedness.

Signed-off-by: Pekka Enberg <penberg@kernel.org>