Allow tabstop and shiftwidth values to be customizable

[kshenoy]

The plugin sets the values of tabstop and shiftwidth to 3 by default. Please make this option customizable.

It would be nice if the plugin allows you to specify these as an option and if the option is not set, use the defaults.

[acornejo]

+1 for this feature, also 3 is a particularly unusual default (2 and 4 seem to be much more common)