No syntax highlighting in included c_cpp files

Hello,

I'll be honest. I don't know what information you need. I am using the code, like so:

```
[import:1-, unindent:"true", lang="c_cpp"](code/c/example.c)
```
There is no syntax highlighting in this case, but when using the exact same importing scheme and another language, it works fine, for example:

```
[import:1-, unindent:"true", lang="csharp"](code/c/example.cs)
```

I have tried both `c` and `cpp` for `.c` and `.cpp` files respectively, but these do not seem to work. I fear I might be missing something in the documentation, but I don't know where to look. Could someone point me in the right direction to solve this issue?

Note that this is with the default settings. Ace will not work for our purposes because it doesn't seem to work with the theme-api. That is, when changing our theme, we should also change the language we are reading in from a file somewhere. When doing this with ace, only the initial language is displayed. When changing the language, no codeblock appears.

If I understand correctly, c/c++ syntax highlighting was fixed for ace (but not for default) in issue #21?

使用預設設定重現兩個匯入範例，並比較 c_cpp、c、cpp 和 csharp 語言路徑；issue #21 是相關參考。完成的標準是，包含的 C 和 C++ 檔案在預設設定下獲得語法醒目提示，同時主題變更仍能正常運作。

由索引模型根據 Issue 內容生成。