Configurable indentation for generated air

[coder11]

Currently nested statements are indented by 1 space everywhere the air used. That makes reading and debugging the scripts difficult (I always indent everything to 4 spaces before starting to do anything with the script), especially when they are embedded as text in .ts files.

Suggestion: increase the default indentation to 4 spaces or make it configurable via a switch. It will improve the "debuggability" of the air scripts