feat: the ability to receive photo/document messages and download files

[DanArmor]

Added

• PhotoSize, File and Document types according to telegram-api
• get_file function to get File object and download_file to download file by file_path from File
• photo and document fields for message
• photo and document methods for update similar to text
• Matcher for Photo and Document messages changed match_update how it handles Message to catch photo/document messages, changed Matcher::match_str to return false on Photo and Document
• added examples - simple bots. One downloads sent files, the other downloads sent photos

Notes:

I was not sure, how to handle downloading, because we need to use https://api.telegram.org/file/bot<token>/<file_path> and not a base_url, and also there is no json-body in request - so I made a download_file method for Client.

[0xfe]

Thanks for the PR. Downloading is a bit of an outlier, and this approach looks fine for now. See minor nitpick.