Port char-width

[A6GibKm]

Closes #1151.

The code works but to run I have to manually remove char-width from bindings.rs to avoid

error[E0428]: the name `char_width` is defined multiple times
     --> src/../generated/bindings.rs:28333:5
      |
28333 |     pub fn char_width(arg1: ::libc::c_int, arg2: *mut Lisp_Char_Table) -> isize;
      |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `char_width` redefined here
      | 
     ::: src/remacs_sys.rs:92:5
      |
92    |     pub fn char_width (c: libc::c_int, dp: *mut Lisp_Char_Table) -> ptrdiff_t;
      |     -------------------------------------------------------------------------- previous definition of the value `char_width` here
      |
      = note: `char_width` must be defined only once in the value namespace of this module

I could use the definition in the bindings but I am not sure on what is the difference between ptrdiff_t and isize and if the use of c_int is fine.

[db48x]

This is good work, but it can be improved slightly

[A6GibKm]

I am currently running make check. Will post when ready.

[db48x]

Now it's perfect!