Minor documentation tweaks:

Remove some excess whitespace. (hmp)
Hyphenate trade-off. (hmp)
Rename "Definitions" to "Glossary. (hmp)
Mark up file names and structure fields better. (hmp)
Improve documentation of credential handling semantics. (rwatson)

Portions submitted by: Hiten Pandya <hiten@unixdaemons.com>