* Overloaded AddModuleAsync with Type

* Overloaded RemoveModuleAsync with Type

* Use expression-bodied method for consistency

Resolves #584

never overestimate the end user

Fixes #487

Implement configurable command node separators

This fixes #304 over foxbot's PR for the same issue.

Parameter preconditions and typereader overriding

Fix case insensitive commands forcing parameters to return lowercase

This commit also adds a TypeReaders property to CommandService, so
it is possible to see all of the registered TypeReaders. This makes
it possible for users to implement their own parsing instead of
using the built-in parsing.

Currently, commands are case-sensitive. This PR allows for commands to be case insensitive (which is now the default option).

Conflicts:
	src/Discord.Net.Commands/CommandService.cs

This adds an (optional) CommandServiceConfig, as well as a DefaultRunMode for commands.

This resolves #368 (for commands where a RunMode is not explicitly specified, a custom default value should be used)

In theory this should just work, more testing is needed though

TypeInfo.BaseType will likely return the same Type if all modules derive from
ModuleBase or some common subclass of it. Making it appear as if only one module
is registered.

Changed to TypeInfo.AsType for expected behavior.

Exclude abstract types from being loaded as modules.