bel parameter help enhancements

[wshayes]

BEL parameters - any function arguments or options
BEL argument - required parameter for a BEL function
BEL option - non-required or optional parameter for a BEL function

BEL entity - :! - special type of BEL parameter
BEL namespace - type of identifier pool, e.g. Entrez Gene, Swissprot, MESH, etc
BEL identifer - specific, primary identifier for BEL entity
BEL label - human-friendly label used for BEL entity (optional - and new with BEL 2.2)