Needed by kdancybot/kdancybot#1

Two possible solutions:

1. Add map data to np command response directly.
2. Add another command (e.g. get-file), which will accept path to .osu file as one of the arguments.

For 2nd solution, we'll need to rework how command are being passed from server.

As mentioned in kdancybot/np-server#1, in near future commands' format will change from string to json. We need to change command's parsing code accordingly.
It is also important to not break compatibility with the old format.

Good solution would be try parsing both formats and use whichever format works.
Release of the updated version of np-client should be earlier than release of np-server's kdancybot/np-server#1 version so everyone will have time to update their clients.

NP client is going to be ran from different folder in the future, so it would be good to add this feature beforehand

Currently we use HTTP GET request. For gosumemory it works fine as response's delay is usually less than 200ms.
On other hand, StreamCompanion often takes a lot of time to respond and sometimes even takes exceeds 2s timeout (which should be more than enough!).

Only fix I can think of right now is changing connection to websockets, so we can be certain we'll get some data (although it may be outdated).