Context: adds router context implementation
Adds router context implementation for coordinating all of the I2P router components:
- Transport (NTCP2)
- I2NP
- End-to-end (garlic/ECIES-X25519) sessions
- NetDB
- Tunnels
Also, adds updates for Proposal 144: ECIES-X25519, Elligator2, and other global refactors.
Changes included in this branch serve as the alpha-0.0.1 release candidate.
Resolves #22 (closed) and #25 (closed)