Replace p_context_init() with p_context_new()/p_context_delete()

spec/test_start_rule_tree.d

@@ -10,10 +10,10 @@ int main()
 unittest
 {
     string input = "hi";
-    p_context_t context;
-    p_context_init(&context, input);
-    assert_eq(P_SUCCESS, p_parse(&context));
-    Top * top = p_result(&context);
+    p_context_t * context;
+    context = p_context_new(input);
+    assert_eq(P_SUCCESS, p_parse(context));
+    Top * top = p_result(context);
     assert(top.pToken !is null);
     assert_eq(TOKEN_hi, top.pToken.token);
 }