Add flowbits feature from Snort/Suricata

[Xumeiquer]

Adding this feature will allow MoleIDS to detect multi-phase attacks.

It could be implemented adding a new entry in the meta section, for example:

rule dummy {
    meta:
        // ...
       flowbits = "set:variable, isset:variable, unset:variable"
    // ...
}

The meta entry flowbits will be a comma separated string with key:value options. The key will be the operation against the flowbits and the value will be the variable where the action takes effect.

It will be also possible to reuse operations, like set:var1, set:var2.