BotkitPlugin interface not strongly typed for optional functions

[roeintense]

botkit/packages/botkit/src/core.ts

Line 163 in 59fb835

export interface BotkitPlugin {

Hey Ben, trying to Typescript up a plugin with the idea that it returns the BotkitPlugin type, per the source, but that interface doesn't have properties to cover any additional functions added as the third or more properties of the object returned inside the plugin.

Thanks bud. Will attempt related PR shortly.