Allow variable updating via messages

Add the ability via configuration to allow variable updating via SMS.  The message format is "set <variableName> to <value>".  This should not interfere with any current triggers unless it is that exact message.

Reply via SMS to the sender for confirmation and errors is included.

Replaced all \t with soft spaces.

Documentation updated.

NOTE: This PR will conflict with #6.  After merging one of them I will rebase the other for a clean merge.  Both update the plugin version to 1.2.0.

Closes #4