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.

Previously, if a user autoloaded commands more than once, commands that were already in the command map would be readded. 

If the module list already contains a module with the same type as the module being loaded, it will not load the new instance of this module.

[Untested] Assembly Crawler will now accept constructors matching: new(), new(CommandService), new(IDependencyMap).

Add IDependencyMap

Add DependencyMap

[UNTESTED] Adds an optional parameter to the Module attribute, "autoload", which defaults to true.

Specifies whether or not the assembly crawler should load this module.