Do not use EventCount to track whether an "unregistered" event
was generated, because that by definition came from a different app
than the one that "owns" that field.

This just adds a separate field to track that state, so it doesn't
potentially modify the counter for an unrelated app.

Instead of identifying a memory pool by its memory address,
use a resource ID.  IDs are a constant size, regardless of
whether the host machine is 32 or 64 bits.

- IDs can be put into commands/telemetry and maintain a more
  consistent format with consistent alignment requirements.
- IDs can be independently verified without dereferencing
  memory.  Previously the only way to validate a memory pool
  was to read the address pointed to, which results in a SEGV
  if the address was bad.

Move the AppID lookup to be early in the CFE_SB_SendMsgFull implementation.
Avoids double locking between SB+ES and avoids a block-scope local variable.

Fix #897, EVS unregistered AppID

Fix #923, Perform appid lookup early

Fix #651, Use resource ID for memory pools

Also check/ensure null termination of output

Fix #705, Use cFE defines to size arrays

Fix #888, Add typedef for function return status codes

Corrects doxygen links to symbols which have been updated