Official announcement: https://core.telegram.org/bots/2-0-intro
Changelog: https://core.telegram.org/bots/api-changelog

• New inline keyboards with callback and URL buttons. Added new objects InlineKeyboardMarkup, InlineKeyboardButton and CallbackQuery, added reply_markup fields to all InlineQueryResult objects. Added field callback_query to the Update object, new method answerCallbackQuery.
• Bots can now edit their messages. Added methods editMessageText, editMessageCaption, editMessageReplyMarkup.
• Bots can request location and phone number from the user. The keyboard field in the object ReplyKeyboardMarkup now supports KeyboardButton, a new object that can have the fields request_location and request_contact.
• Added support for all content types available on Telegram. 19 types of InlineQueryResult objects are now supported.
• Inline bots can now subsitute all kinds of content with text. Added 4 types of InputMessageContent objects.
• You inline bot can also ask users for permission to use their location. Added the new Botfather command /setinlinegeo, added field location to the InlineQuery object, added fields location and inline_message_id to the ChosenInlineResult object.
• Added an easy way to switch between inline mode and a private chat with the bot – useful for settings, establishing external connections and teaching users how to use your bot in inline mode. Added parameters switch_pm_text and switch_pm_parameter to the method answerInlineQuery.
• Added group administration tools. New methods kickChatMember and unbanChatMember.
• Added fields venue, pinned_message and entities to the Message object. Added new objects MessageEntity and Venue, new methods sendVenue and sendContact.
• Renamed the fields new_chat_participant and left_chat_participant of the Message object to new_chat_member and left_chat_member.