A.K.A. "FiniteReality is a twat"

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

Parameter preconditions and typereader overriding

Resolves #302

per the following API error:
{
  "bitrate": [
    "Int value should be greater than 8000."
  ]
}

this was a big one

Fix case insensitive commands forcing parameters to return lowercase

Nickname changes/role changes are no longer sent over PRESENCE_UPDATE, making it obsolete to check for changes there.

*facepalm*

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

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

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