Add new features from Bot API 3.3

Merge pull request TelegramBot#78 from Pabloader/pabloader-master

Client::callbackQuery

Add `leaveChat` method

Change phpunit version to ~4.0 to support PHP 5.5 tests

Merge pull request TelegramBot#66 from choldimir/master

Update README.md

Fix editMessageReplyMarkup and editMessageCaption methods.

Add inline_message_id param.

Add caption field to sendDocument method

Merge pull request TelegramBot#59 from pwsdotru/issue-54

Fix issue for call toJson on a non-object

Merge pull request TelegramBot#56 from vitorbari/patch-callback-query

Patch CallbackQuery

Added InlineKeyboardMarkup support