A.2 use kcp+smux as a transport for obfs4

this issue will be considered done when:

1. obfsvpn gains the capability to use a kcp transport for the obfs4 PT.
2. this ability is properly documented and end-to-end tested.

the cli version of the kcptun tunnel can be used for reference: https://github.com/kalikaneko/kcptun-shapeshifter

Subissues for this deliverable are:

• #10 (closed) Use kcp Dialers and Listeners.
• #11 (closed) Document possible transports.
• #12 (closed) Add example code for obfsvpn server.

Beyond unit-testing, any e2e tests should include the ability to generate valid key material for the obfsproxy configuration (perhaps the easiest thing is to do a first run that generates the state, as obfsproxy does). Also be aware that we need integration tests with the openvpn reference implementation: in the past, we've observed that e2e tests using netcat or similar do not catch framing issues that avoid the openvpn handshake to be completed.