Changes

Javadoc and cleanup (#249)
* Reformated the the documentation for the JDA object.
error in a few files `preform` -> `perform`
doc.

* Cleaned up the implementation of EmbedBuilder.
Cleaned up the documentation in EmbedBuilder, JDABuilder, Permission,
Region, and OnlineStatus

* Cleaned up the documentation in MessageBuilder

* Added docs to emotes/reactions/webhooks/presence

* Adjusted Utility docs

* Adjusted docs for Game/Icon, added some @author tags

* Adjusted docs for (most) entity classes

* Removed double "this this" in javadoc of JDA#getUserById()

* Added full javadoc to MessageHistory.
entities package.
now lives only as a default method in MessageChannel.
target="_blank" to some href links.

* Fixed documentation error and added (and formatted) javadoc excludes.

* Wrote javadoc for the audio.factory package.

* Added javadocs for `audio.hooks`

* Formatted javadoc for `audio` to follow new javadoc format.

* Fix typo

* Added documentation to EventManager/EventListener classes

* First pass on core.entities javadoc. AudioChannel - Guild.
documentation for requests.restaction
MFA accounts.
DEFAULT_SUCCESS and DEFAULT_FAILURE non-final.

* Second pass on core.entities javadoc. GuildVoiceState - Message.
Added Message#delete(), deprecated Message#deleteMessage().
Permission checks for adding reactions from Message to MessageChannel.
Changed over some exception to IllegalStateException, a more valid
representation of the error.

* JavaDoc pass for managers

* Made MessageBuilder implement Appendable and removed its deprecated
methods. Fixed javadoc errors

* Documented and restructured MessageChannel.
between TextChannelImpl, PrivateChannelImpl, and GroupImpl related to
MessageChannel and moved it into default methods in MessageChannel.
Permission checks now exist in TextChannelImpl overrides with calls to
MessageChannel's default methods after checks.
JDABuilder#setToken documentation for AccountType.CLIENT.

* Completion of core.entities javadoc.

* Fixed javadoc errors, ran spelling checker and added docs to
core.exceptions

* Added docs related to being blocked by the recipient of a
PrivateChannel

* Updated copyright
 (commit: d109ee4)