Should I bind manually instead of bindgen?

Currently, there are the following issues about `bindgen`:

* The types of most constants are incorrect.
* Sometimes we need the *new type* pattern instead of the type alias. For example, `mbool` might conflict with `mint` in a 32-bits platform.
* Maybe we want to use `feature` to select the version of Wolfram LibraryLink, and `bindgen` doesn't seem to be so flexible for this situation.
