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.

Seems I missed this originally, whoops.

The previous name was causing some confusion

EmbedBuilder.WithImageUrl() now uses the value passed

Add TimeSpan TypeReader

Adds Timestamps to embeds, and removes Image and Thumbnail-Builders

Add configuration option for case insensitive commands

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

Close the WebSocket when disconnecting

Throw an exception when creating a Color with an invalid float value

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

For a command to use the DefaultRunMode, it must now have it's RunMode set to RunMode.Default (this is the default value on CommandAttribute now).

This prevents a 400 when sending a malformed color to Discord.

ModifyAsync will accept an EmbedBuilder

Add CommandServiceConfig, DefaultRunMode

**This is not a breaking change**.

This change begins to implement #379, where IUserMessage.ModifyAsync will now accept a `Discord.ModifyMessageParams` func over a `Discord.API.Rest.ModifyMessageParams` func.

This resolves #224

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)

This is a breaking change.

Adds a precondition that requires the bot has a specified permission (Resolves #211).

Renames RequirePermission to RequireUserPermission.

This precondition will require that the invoker of the command is the owner of the bot.