Adds first version of `processContentOffset'

This commit also includes an example application on how to use the
`processContentOffset' method.

examples/reading_logs_with_offset/read.cc

@@ -0,0 +1,34 @@
+
+#include <stdio.h>
+#include <string.h>
+
+#include <modsecurity/modsecurity.h>
+
+
+// Variable offset - REQUEST_HEADERS_NAMES
+
+const char *request = "" \
+    "GET /index.html?param1=value1&param2=value1&param3=value1 HTTP/\n" \
+    "AuThOrIzAtIoN: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==\n" \
+    "Host: localhost\n" \
+    "Content-Length: 27\n" \
+    "Content-Type: application/x-www-form-urlencoded\n";
+
+
+int main() {
+    modsecurity::ModSecurity msc;
+    std::string json("");
+    const char *err = NULL;
+    int ret = 0;
+
+    ret = msc.processContentOffset(request, strlen(request),
+        "o0,4v64,13v114,4v130,14v149,12t:lowercase", &json, &err);
+
+    if (ret >= 0) {
+        std::cout << json << std::endl;
+    } else {
+        std::cout << err << std::endl;
+    }
+
+    return ret;
+}