Add vless protocol in vmess2json.py

[recolic]

This PR does 3 work:

1. Refine code to use dedicated function for base64 decoding.
2. Add logic to parse vless link.
3. Remove embedded DNS server and routing settings, which is confusing.

It solves #13

[recolic]

Tested with the following testcases:

ss://Y2hhY2hhMjAtaWV0Zi1wb2x5MTMwNToxMTExMjIyMkB1czEubmQ6MjU1NTE#REMARK
vless://11111111-1111111111111111111@sg2.mydo.com:443?path=%2Fvideo&security=tls&encryption=none&host=sg2.mydo.com&type=ws&sni=sg2.mydo.com#MY_GREAT_WALL
vmess://ewoidiI6ICIyIiwKInBzIjogIlRFU1RJTkciLAoiYWRkIjogInJ0ZXN0LTEtMS0xLTEuZnJlZW15aXAuY29tIiwKInBvcnQiOiAiNDQzIiwKImlkIjogIjdjMTExMTExMTExMTExMTExMTExMTExMTExMTEiLAoiYWlkIjogIjAiLAoibmV0IjogImgyIiwKInR5cGUiOiAibm9uZSIsCiJob3N0IjogInJ0ZXN0LTEtMS0xLTEuZnJlZW15aXAuY29tIiwKInBhdGgiOiAiL2NkbiIsCiJ0bHMiOiAidGxzIgp9Cg==

All of them looks good.