Added a c_char implementation

Author: elichai

src/types.rs

@@ -4,6 +4,9 @@ use core::fmt;
 pub type c_int = i32;
 pub type c_uchar = u8;
 pub type c_uint = u32;
+
+/// This might not match C's `c_char` exactly.
+/// The way we use it makes it fine either way but this type shouldn't be used outside of the library.
 pub type c_char = i8;
 
 /// This is an exact copy of https://doc.rust-lang.org/core/ffi/enum.c_void.html