Added usage statement, changed grep/sed/awk commands to use a regex that...

Added error message when incorrect number of arguments passed.  Added usage statement, changed grep/sed/awk commands to use a regex that does a more explicit match rather than simply a substring match.  This should help prevent accidental partial matches.  Also replaced a couple points where the cpanel.config location was hard-coded instead of using the variable.  Added quotes around certain variable names to prevent accidental evaluation of arguments (ie: SecurityPolicy::xml-api).  Changed the grep conditions to use the "-q" flag rather than >/dev/null.
Got fancy with regex to prevent accidentally setting all values from "0" to "1", for example.  We just want to substitute $cvalue with $value on the line that starts with "$name=".