The following environment variables are required:

COIN          - see lib/coins.py, must be a coin NAME
NETWORK       - see lib/coins.py, must be a coin NET
DB_DIRECTORY  - path to the database directory (if relative, to run script)
USERNAME      - the username the server will run as
SERVER_MAIN   - path to the server_main.py script (if relative, to run script)

In addition either RPC_URL must be given as the full RPC URL for
connecting to the daemon, or you must specify RPC_HOST, RPC_USER,
RPC_PASSWORD and optionally RPC_PORT (it defaults appropriately for
the coin and network otherwise).

The other environment variables are all optional and will adopt sensible defaults if not
specified.
