Telegram Handler: support additional API parameters

[Pascal-So]

The telegram API for sendMessage supports some additional parameters that where not yet covered with the current implementation. See the API documentation here:

https://core.telegram.org/bots/api#sendmessage

In my use case I'm mostly just interested in the parse_mode parameter but I thought that while I'm on it I could also add support for disable_web_page_preview and disable_notification.

I didn't add support for the other remaining options because in my opinion they will never make sense when using the API for logging. reply_to_message_id can only be set for replies, but when logging we're not replying to a message but rather sending independent messages. reply_markup lets the bot display an interactive interface for the user receiving the message, but the log handler can't deal with replies anyway.

Something that I'm not sure about whether it's okay like this is the function argument order to the constructor. Should I move the new arguments to the end?

[Pascal-So]

I've added some simple validation for the parse mode in the setter, plus tests for the validation.

[Seldaek]

Thanks for the updates!