Added -o, --vars-optional args (variables no longer required)

[svpease]

When a file is fed to templater.sh to replace variables within the template but the template has no variables to replace, the expected behavior would be to print out the file as is. I've added this new argument to not change existing behavior but allow for the option to no longer require variables within the file. This is handy if you have a folder of files that may or may not need variable substitution.