Capitalisation:
- The option is lower case `--logmetrics` but help said `--logMetrics`
- Same for `--logmetricsiterval`
- Same for `--metricsserver` and `--metricsserverport`
Ethereum network selection:
- Moved out into their own, cleaner help section
- Added help for `--mainnet`, `--goerli` and `--kovan`
- Moved `--networkid` and `--customnetwork` to this section as well
Other:
- Reworded or formatted some help lines for clarity and consistency
Changed options:
- Renamed `--metricserver` to `--metrics`
- Renamed `--matricsserverport` to `--metricsport`
- Removed Morden network; this didn't have an option, but could be
selected with `--networkid:2` and then fail to work
Signed-off-by: Jamie Lokier <jamie@shareable.org>