Adds PoC about 1-time variable resolution and draft for offset

There is no need for the variable purely associated with the
transaction (transient) be part of collection that demands
lookups. Also, those variables will held the concept of offset:
The offset from the first byte of the request till the start of
the variable.

headers/modsecurity/transaction.h

@@ -86,8 +86,51 @@ class Operator;
 }
 
 
+class AnchoredVariable {
+ public:
+    AnchoredVariable(Transaction *t, std::string name)
+        : m_offset(0),
+        m_name(name),
+        m_transaction(t),
+        m_value("") { }
+    size_t m_offset;
+    std::string m_value;
+    Transaction *m_transaction;
+    std::string m_name;
+
+    void set(const std::string &a, size_t offset) {
+        m_value = a;
+        m_offset = offset;
+    }
+
+    void append(const std::string &a, size_t offset,
+        bool spaceSeparator = false) {
+        if (spaceSeparator && !m_value.empty()) {
+            m_value.append(" " + a);
+        } else {
+            m_value.append(a);
+        }
+        m_offset = offset;
+    }
+
+    void evaluate(std::vector<const collection::Variable *> *l) {
+        l->push_back(new collection::Variable(&m_name,
+            &m_value));
+    }
+};
+
+
+class TransactionAnchoredVariables {
+ public:
+    TransactionAnchoredVariables(Transaction *t)
+        : m_variableArgsNames(t, "ARG_NAMES") { }
+
+    AnchoredVariable m_variableArgsNames;
+};
+
+
 /** @ingroup ModSecurity_CPP_API */
-class Transaction {
+class Transaction : public TransactionAnchoredVariables {
  public:
     Transaction(ModSecurity *transaction, Rules *rules, void *logCbData);
     ~Transaction();
@@ -376,7 +419,6 @@ class Transaction {
 
  private:
     std::string *m_ARGScombinedSizeStr;
-    std::string *m_namesArgs;
     std::string *m_namesArgsGet;
     std::string *m_namesArgsPost;
     std::string *m_requestHeadersNames;