add support for external plugins to get custom arguments.

[ShadowKnightMK4]

add support for external plugins to get custom arguments (update the usage text also!).

Currently this does not do this.

Note this would need to have two things done.

1, the front end would need to be able parse it (such as /arg="something=value" and so on)

2, the class library used by the front end (OdinSearch) would need to have code to propagate the plugin info.

Note 100% committed to the minor update for this but may consider it if it's trivial enough.

[ShadowKnightMK4]

Not off the table. May be punted to version 2.0