although already used when setting up webhooks, the parameters
allowed_updates and max_connections were actually never passed to the
api.

The certificate and privateKey are required values since they're used
unconditionally when using webhooks.
The url and host are optional but at least one of them has to be defined
and using '0.0.0.0' as a default value for host would cause an invalid
url to be autogenerated otherwise.

reply_markup actually only accepts JSON-serialized objects. For user
convenience simply JSON.stringify() passed objects on demand.

This adds type declarations to the library making it fully typed for
TypeScript support

The request data was actually serialized as multipart/form-data instead
of a JSON body. Passing JSON data with a boolean value then throw an
error while serializing:

bot.sendMessage({
	chat_id: user.id,
	text: text,
	disable_web_page_preview: false, // throws an error
});

// > TypeError [ERR_INVALID_ARG_TYPE]: The first argument must be one of type string or Buffer. Received type boolean