Improve documentation of abort functions
Improve documentation of abort functions

Explicitly state that calling abort is safe after initializing to
zero.

Explicitly state that calling abort on an inactive operation is safe,
and replace "active" by "initialized" in the description of the
parameter.

Get rid of the recommendation for implementers to try to handle
uninitialized structures safely. It's good advice in principle but
cannot be achieved in a robust way and the wording was confusing.

ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls