Change default max_connections to 200

This is to support the benchmark, which runs with 200 connections.
Unfortunately, because Ftpd currently does not do streaming file i/o,
more connections makes it easier for clients to cause Ftpd to run out
of memory.  However, streaming file i/o, which is planned, will fix
that.
FtpServer attributes in alphabetical order
Bits of cleanup to the Readme
Document all server attributes.
Note compliance with another requirement of RFC-2577
Note that port stealing protection is (and has been) in place
Disconnect after failed logins (configurable)