Feature request: Support for macros

Hi!

**Current situation**
I am using this new feature to have columns for iterations described here #39
Although I would like to use the macro _@CurrentIteration_ to get dynamically always the current sprint and next sprint per column.
For the moment this is hardcoded with the Sprint name.

**Expected bahavior**
In the JSON-document I could write the macro to dynamically get the current sprint
with for example: ` "name":"\\@CurrentIteration"`

I doubt this is already supported but this would definitely be a nice addition to have!