Adds support to suspicious and whitelist to Read and Write limits

The operators @ipMatch, @ipMatchF and @ipMatchFromFile were
added to the functions: SecReadStateLimit and SecReadStateLimit,
by using them it is possible to declare a suspicious list. When
a suspicious list is given, the {Read|Write}StateLimit will be
applied just to the IPs that belongs to that restricted list.
Note that the negative of those operators (e.g. !@ipMatch) can be
used to place a whitelist. The {Read|Write}StateLimit
restrictions will not be applied to those in the whitelist.
This current version the Sec{Read|Write}StateLimit can be used
varios times to add elements to both lists, however, the
last informed limit will be applied for the entire group. This
feature is experimental, and suggestions on how to improve it
are very welcome. For further discussion use the issue: #353.
Bugfix: Missing ipv6 support check

The Function "ip_tree_from_file" was making a reference for
IPV6_TREE whitout checkingx if it was supported or not.
Using RadixTree instead of list to storage IPs

Used by the operator @ipMatch and variants, this structure storage all the IPs
addresses for later comparison. Last version was using RadixTree only if the
set of IPs was specified from files. IPs specified as parameters, was using
a chained list. Chained lists may affect the performance, since lookups in
worst case will be O(n). RadixTrees could provide better results depending
on the amount of elements and its contents.
Honor the SecRuleEngine while filtering connections

The SecRuleEngine has the capability to Enable, Disable or even to place the
ModSecurity in DetectionOnly mode. The SecReadStateLimit and SecWriteStateLimit
were not honoring such state, due the fact that our configuration belongs to
requests not to connections, the only struct that exists while those filters
are placed. By adding a global variable "conn_limits_filter_state" we are now
able to identify the current state of the ModSecurity, once the configuration
is loaded this variable is set and used by the connections filters.
Places connection filter engine in a separated configuration

Different from the Rules or other options, the connections filters are applied
to entire server, not to a single vhost, or so. In order to keep it clear to
the user this patches adds "SecConnectionEngine" which works in the same way
that SecRuleEngine does.
Renames Sec{Read|Write}StateLimits

The Sec{Read|Write}StateLimits are filters related to the connections, when the
server did not know yet which vhost the request goes to. This means that once
those configrations are set it will be applied to entire server. This patch
just renames the Sec{Read|Write}StateLimits to SecConn{Read|Write}StateLimits
to make it more clear to the user. SecConnectionEngine was also renamed to
SecConnEngine.