Miscellaneous changes in the API

[unreal4u]

More power to admin bots

• unbanChatMemeber now also works in channels!
• New method deleteMessage that allows the bot to delete its own messages, as well as messages posted by other in groups and channels where the bot is an administrator.

Minor Changes

• Replaced the field new_chat_member in Message with new_chat_members (the old field will still be available for a while for compatibility purposes).
• Inline keyboards with switch_inline_query and switch_inline_query_current_chat can no longer be sent to channels because they are useless there.
• New fields gif_duration in InlineQueryResultGif and mpeg4_duration in InlineQueryResultMpeg4Gif.