Added REST API endpoints for forge, repo and issue information

[gridhead]

Can be used for asynchronously fetching and updating the DOM.

How do you test?

1. Follow the setup instructions on the README.md to generate a JSON index and start the server.
2. Run the following commands and notice their outputs.

   from urllib3 import PoolManager
   from json import loads
   httpobjc = PoolManager()
   respobjc = httpobjc.request("GET", "http://localhost:9696/endpoint/")
   loads(respobjc.data.decode())

   from urllib3 import PoolManager
   from json import loads
   httpobjc = PoolManager()
   respobjc = httpobjc.request("GET", "http://localhost:9696/endpoint/", fields={"command":"PREL"})
   loads(respobjc.data.decode())

   from urllib3 import PoolManager
   from json import loads
   httpobjc = PoolManager()
   respobjc = httpobjc.request("GET", "http://localhost:9696/endpoint/", fields={"command": "REPO", "forge": "gitlab", "repository": "t0xic0der/fragment"})
   loads(respobjc.data.decode())

   from urllib3 import PoolManager
   from json import loads
   httpobjc = PoolManager()
   respobjc = httpobjc.request("GET", "http://localhost:9696/endpoint/", fields={"command": "TICK", "forge": "gitlab", "repository": "t0xic0der/fragment", "number": 11})
   loads(respobjc.data.decode())

See if it works.

[gridhead]

@nphilipp, see if some more things need to be changed.