Move some messages to 'chatty' (from 'debug')
Docs
Retry bootstrapping after delay if it fails
markup fix
Multiple changes

- Add timeout to node cleanup procedure (to avoid blocking indefinitely
  on sending ShuttingDown signal)
- Client pool API: Add checking whether a pool is full
- LDCs, direct channels from the node pool to its nodes, introduced.
  This makes it much easier to inject messages into the network, e.g. by
  the bootstrap server.
- Restarting MVar for the node pool introduced. When filled, one node is
  restarted.
Make better use of STM for new Incoming edges
Handshake implemented

Handshakes are a rewrite of the connection establishment procedure.
Contrary to the "IAddedYou/AddMe"-based procedure, which was a bit too
asynchronous, the new method makes sure both parties are OK before a new
connection is established. This should drastically reduce the amount of
one-sided (zombie) connections, and eliminate excessive connections
from/to a single node because of timing issues.