Maintain existing error message for not-enough-args
Add "too many args" if too many args
Add more helpful error message if v2 syntax was used
New output:
```
sauer@host:~/dev/etcd$ ./bin/etcdctl --endpoints http://localhost:5001 member add
Error: member name not provided.
sauer@host:~/dev/etcd$ ./bin/etcdctl --endpoints http://localhost:5001 member add node2 node2
Error: too many arguments
sauer@host:~/dev/etcd$ ./bin/etcdctl --endpoints http://localhost:5001 member add node2 http://localhost:6002
Error: too many arguments, did you mean "--peer-urls http://localhost:6002"
sauer@host:~/dev/etcd$ ./bin/etcdctl --endpoints http://localhost:5001 member add http://localhost:6002 node2
Error: too many arguments, did you mean "--peer-urls http://localhost:6002"
```
In cases of multiple endpoints, it's possible member add would get a its
member list from a member that has not yet recognized the membership
update. Instead, confirm that the member list response is from the
member that acked the member add or from a member that has synced
with the cluster following the member add.
Fixes#7498
Documentation was far too repetitive, making it a chore to read and
make changes. All commands are now organized by functionality and all
repetitive bits about return values and output are in a generalized
subsections.
etcdctl's output handling was missing a lot of commands. Similarly,
in many cases an output format could be given but fail to report
an error as expected.
