Trip comment to 80 cols in SentinelCommand().
Add all the configurable fields to addReplySentinelRedisInstance().

Note: the auth password with the master is voluntarily not exposed.
Sentinel: added SENTINEL MASTER <name> command.

With SENTINEL MASTERS it was already possible to list all the configured
masters, but not a specific one.
anetResolveIP() added to anet.c.

The new function is used when we want to normalize an IP address without
performing a DNS lookup if the string to resolve is not a valid IP.

This is useful every time only IPs are valid inputs or when we want to
skip DNS resolution that is slow during runtime operations if we are
required to block.
Sentinel: SENTINEL MONITOR command implemented.

It allows to add new masters to monitor at runtime.
anetResolveIP() prototype added to anet.h.
Sentinel: flush config on disk when new master is added.
Sentinel: releaseSentinelRedisInstance() top comment fixed.

The claim about unlinking the instance from the connected hash tables
was the opposite of the reality. Also the current actual behavior is
safer in most cases, so it is better to manually unlink when needed.
Sentinel: SENTINEL REMOVE command added.

The command totally removes a monitored master.
Sentinel: fix wrong arity error message.
SENTINEL SET implemented.

The new command allows to change master-specific configurations
at runtime. All the settable parameters can be retrivied via the
SENTINEL MASTER command, so there is no equivalent "GET" command.
SENTINEL SET: error on bad option name + flush config on error.