Update usage message.

jsonget users -file, not -f.
Add '-silent' flag for suppressing errors.

Errors will sill return a non-0 exit code.
Update changelog.
Small code and documentation cleanups.
Add wildcard support.

This allows you to loop through arrays nicely.
Add docs for wildcards.
Add another wildcard example to the readme.
Fix readme formatting.
Simplify splitAttributeParts()