Redesign asset retrieval in the library.

Most assets now return a new class named `Asset`. This allows for the
assets to be consistently saved via a `save` method instead of special
casing for `Attachment`.

`AppInfo` is no longer a namedtuple it is a fully documented dataclass,
as well as having the state attached to it.

Fixes #1997

discord/appinfo.py

@@ -0,0 +1,73 @@
+# -*- coding: utf-8 -*-
+
+"""
+The MIT License (MIT)
+
+Copyright (c) 2015-2019 Rapptz
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+"""
+
+from .user import User
+from .asset import Asset
+
+
+class AppInfo:
+    """Represents the application info for the bot provided by Discord.
+
+
+    Attributes
+    -------------
+    id: :class:`int`
+        The application ID.
+    name: :class:`str`
+        The application name.
+    owner: :class:`User`
+        The application's owner.
+    icon: Optional[:class:`str`]
+        The icon hash.
+    description: Optional[:class:`str`]
+        The application description.
+    bot_public: :class:`bool`
+        Whether the bot is public.
+    bot_require_code_grant: :class:`bool`
+        Whether the bot requires the completion of the full oauth2 code
+        grant flow to join.
+    rpc_origins: Optional[List[:class:`str`]]
+        A list of RPC origin URLs, if RPC is enabled.
+    """
+    __slots__ = ('_state', 'description', 'id', 'name', 'rpc_origins',
+                 'bot_public', 'bot_require_code_grant', 'owner', 'icon')
+
+    def __init__(self, state, data):
+        self._state = state
+
+        self.id = int(data['id'])
+        self.name = data['name']
+        self.description = data['description']
+        self.icon = data['icon']
+        self.rpc_origins = data['rpc_origins']
+        self.bot_public = data['bot_public']
+        self.bot_require_code_grant = data['bot_require_code_grant']
+        self.owner = User(state=self._state, data=data['owner'])
+
+    @property
+    def icon_url(self):
+        """:class:`.Asset`: Retrieves the application's icon asset."""
+        return Asset._from_icon(self._state, self, 'app')