Add better support for F#

DrillSergeant makes heavy use of `dynamic` and `Task` behind the scenes when implementing steps. Neither is well supported in F#. By default, the `task` computational expression in F# returns `Task` and the closest equivalent to `dynamic` is to cast back to `IDictionary` and overload the `?<-` operator.

We should add additional bindings that are more friendly to F#. This could include an auxiliary hooks library to predefine short-hands and/or generate additional overloads to the behavior extensions.

No files, tests, or entry points are named. Start by locating the behavior extensions that use dynamic and Task, then determine which F# bindings or overloads are needed; done means F# callers can use the step implementation without the stated dynamic and Task limitations.

Written by the indexing model from the issue text.