[parser] moving tagger function pointer definition to a separate header so it can be used for other models

src/tagger.h

@@ -0,0 +1,5 @@
+#include "string_utils.h"
+#include "tokens.h"
+
+// Arguments:                           tagger, context, tokenized str,       index
+typedef bool (*tagger_feature_function)(void *, void *, tokenized_string_t *, uint32_t);