Speed-up devcomuino sketch by only reading available data.

There is currently a unneeded 1 second latency inside the sketch used for DevComuino. This removes it.

Currently, DevComuino tries to read enough data to fill the command buffer with a 1 second timeout. Since it will never receive enough data (the buffer is larger than needed), then every single read will require the timeout to expire.

This patch only tries to read the available data (Serial.available) that should be available right away.