Added the history count command to quickly count the number of history
files.
Renamed environment variables to lowercase and added the hosts_history
variable to determine whether the hosts(1) program stores history
information.
Implemented and tested the hosts_history environment variable which can
be used to determine whether history files are created or not.
Updates to the documentation and made attempts to call on with an on
block a silent noop, but kept the exit code >0 likewise for the off
command.