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.
Removes forced chartset

Apperantly forcing the charset is not placing any benefits, instead it is
cousing problems as documented on #650. This still experimental, just
testing against our regression tests. Such feature was added by the commit:
177b5b9c989b0095e5c91b01d205df64e65e6c9e.
Adds initial support to @detectXSS

Libinject was recently updated to support XSS detection. This commit adds
initial support to it.
Updates the libinjection

Windows compilation was failing due to the utilization of size_t which is part
of the strings.h. strings.h was not part of windows and so the compilation
was failing. This update fix that. Issue #65 on libinjection:
https://github.com/client9/libinjection/issues/65
Uses %zu to print size_t instead of %d.

This will help to reduce the amount of warnings during the compilation
See #631 for further information.
Code cosmetics: Reduces the amounts of warning.

Removes the warnings by adding missing headers and removed unused variables.