* Add NullableTypeReader.

Primitives now also load a NullableTypeReader<T> and any value types that get a typereader added will also have a NullableTypeReader<T> added for it.

* Remove unnecessary null check.

* Added docstrings.

* Changed Guild#DefaultChannel to resolve the first accessible channel

Resolves #776

This change is inline with hammerandchisel/discord-api-docs#329

RestGuild#DefaultChannelId is now obsolete and will throw a
NotSupportedException.

* RestGuild#DefaultChannelId will fall back to the guild ID

Adding an exception here would be a breaking change, so this was agreed
to fall back to the previous behavior, which would just return the guild
ID.

IChannel.IsNsfw will now return false when being used on any channel
that is not an ITextChannel. When being used on an ITextChannel, this
will now account for the API flag, and fall back to the channel name.

(this is gross design, thanks discord)

* Fix CreateGuildAsync not doing anything with the input stream for the guild icon.

Also fixes an issue with potential stream types that throw a NotSupportedException when checking its properties. [Apparently, they exist.](https://github.com/dotnet/corefx/blob/master/src/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpResponseStream.cs)

* Merged with old method

* Removed duplicate decl

* Throw when attempting to add or remove a member's EveryoneRole

This resolves #780

* Removed braces

* Update RestRole.cs

Fix everyone mention.

* Update SocketRole.cs

Fix everyone mention.

* I'm good at this, I swear.

Seeing as D.NET will warn you about an impending BadRequest if you try and send an empty field, why not make it warn about the impending BadRequest if you try and send a whitespace field?

This provides tests to ensure the following:
- Creating a Color
- Creating a Default Color
- Accessing a Color's Raw Value
- Accessing a Color's translated RGB values

This resolves #784

* Update client.cs

Let's not have the client be a local variable, hm?

* Update complete.cs

* Update complete.cs

* Update client.cs and complete.cs

Let's not have the client be a local variable, hm?

Fixed RestGuildUser not updating inherited RestUser properties

* Fix potential nullref in embedBuilder value setter

* Null check on footer iconUrl

* Adding checks for the other URL properties

* Adding IsNullOrUri extension

* Setting StringExtensions as internal

* Make ShardedCommandContext derive from SocketCommandContext

* Explicitly re-implement ICommandContext.Client

Why am I such a bad programmer? Maybe I'm just bad with git. Maybe I'm
just bad in general. Maybe I should resign from programming.

* Fix CalculateScore throwing on missing parameters

* Bump to version 1.0.1

* Add embed builder extensions

People in #dotnet_discord-net suggested that this should be part of
the lib after I demonstrated it

* Move some extensions into EmbedBuilder [2]

Apparently git didn't like that previous commit

* Fix error with EmbedBuilderExtensions

A summary of issues which happened:
- Git decided to add an amend commit (I told it to quit?)
- VS Code thinks everything is an error so it wasn't helpful
- dotnet decided to think there was no error until I deleted all
  build outputs and rebuild

Sometimes I question my ability to use version control properly.

* Allow commands to return a Task<RuntimeResult>

This allows bot developers to centralize command result logic by
using result data whether the command as successful or not.

Example usage:
```csharp
var _result = await Commands.ExecuteAsync(context, argPos);
if (_result is RuntimeResult result)
{
    await message.Channel.SendMessageAsync(result.Reason);
}
else if (!_result.IsSuccess)
{
    // Previous error handling
}
```

The RuntimeResult class can be subclassed too, for example:
```csharp
var _result = await Commands.ExecuteAsync(context, argPos);
if (_result is MySubclassedResult result)
{
    var builder = new EmbedBuilder();
    for (var pair in result.Data)
    {
        builder.AddField(pair.Key, pair.Value, true);
    }
    await message.Channel.SendMessageAsync("", embed: builder);
}
else if (_result is RuntimeResult result)
{
    await message.Channel.SendMessageAsync(result.Reason);
}
else if (!_result.IsSuccess)
{
    // Previous error handling
}
```

* Make RuntimeResult's ctor protected

* Make RuntimeResult abstract

It never really made sense to have it instantiable in the first place,
frankly.

* Allow arbitrary attributes to be added to commands

I still don't approve adding type info back into commands, so
I decided to use this solution for allowing arbitrary attributes to be
added to commands.

Add attributes property to ParameterBuilder

Add Attributes properties to info types

* Why on earth git

* Add using for system so that Attribute can be used

* C#7 features in commands, CommandInfo in ModuleBase

* Update TypeReaders with C#7 features and IServiceProvider

* Add best-choice command selection to CommandService

* Normalize type reader scores correctly

* Fix logic error and rebase onto dev

* Change GetMethod for SetMethod in ReflectionUtils

Should be checking against setters, not getters

* Ensure args/params scores do not overwhelm Priority

* Remove possibility of NaNs

* Add DiscordColors struct

* Moved presets to Discord.Color

* Add support for audit log reasons

* Made changes per discussion

Update events.cs, clarify enabling message caching.

PreconditionGroup quick fix

Add 'tweet' embed type