allow to pass custom path and query string to ws connection

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This change allows to set custom query string to the websocket connection.

Example

local ws = websocket_async(true)
ws:connect("ws://0.0.0.0/custom_path?foo=bar")

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Apparently this only works in the browser environment. 😢

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This is now working as expected on https://github.com/britzl/defold-websocket