Change 'trusted applications' to 'privileged applications'.

The word 'trust' can be misused and can have multiple meanings.
The word 'privileged' more accurately describes the concept.

Some additional improvements will be needed to the 'security considerations'
section.
Merge pull request #52 from jplyle/remove-trust-terminology

Change 'trusted applications' to 'privileged applications' and improve some wordings.