Recursive depth argument for cmd line

[EgorWeders]

To see how it works change in main.c laser_list_directory 3 params to value bigger then -1 (-1 prints max available ). You only need to implement cmd parsing for depth value ( int recursive_depth in opt struct for example).

[EgorWeders]

With 0

With 1

With -1 it works like before

[EgorWeders]

Usage : -r0 (only root dir content) , -rN (traverse recursively to max N depth of root dir content), -r (max available depth for root dir)

[jmattaa]

I have added documentation and ability to run --recursive=N using the long argument.