* Add grouping of preconditions to allow for flexible precondition logic.

* Fix checking Module Preconditions twice (and none of the command's own)

* Fix command preconditions group 0 looping over every other precondition anyway #whoopsies

* Use custom message when a non-zero Precondition Group fails.

* Fix doc comment rendering.

* Refactor loops into local function

* Considering a new result type

* Switch to IReadOnlyCollection<T> and fix compiler errors

* Revert PreconditionResult -> IResult in return types - Change PreconditionResult to a class that PreconditionGroupResult inherits.

* Feedback on property name.

* Change grouping type int -> string

* Explicitly use an ordinal StringComparer

* Full stops on error messages

* Remove some sillyness.

* Remove unneeded using.