$increaseChannelVar
To increase channel variable with a certain amount.
If the variable doesn't exist it will be created and its value set to the answer of the value as if the original value of the var is 0.
Usage
$increaseChannelVar[variable name;amount/expression;channel id;default amount (default is 0)]
Example (increase channel messages by 1):
$increaseChannelVar[messages;1]
Example (double the messages):
