using parameter_update.py script

Rename tune_control_s strength to volume to match Nuttx and Linux standard nomenclature for audio (loudness) control.

This is a step towards isolating time from the system.

Generally exit() should not be used on Posix, because it exits the whole
program instead of only the task.

px4_main_t is defined as:
typedef int (*px4_main_t)(int argc, char *argv[]);
which matches with the definition in NuttX, given to task_create

 - px4_add_module now requires MAIN
 - px4_add_library doesn't automatically link

Since assertions lead to crashes, we need better failure handling. In all
the cases in this patch, the assert is not required.

All the ones with the task id should be replaced with the module base
class.

Ah yes, and this reduces flash space, since the ASSERT macro will expand to
a printf that contains the source file name.

This will initialize those structs with zero in all fields not set
and all fields set will only be change once to the final value not
wasting CPU time zeroing it.

This will guarantee that no non-unitialized structs will have
a trash value on from_external causing it to be sent to the
MAVLink channel without need it.

Lets save a few bytes using the right data types.