Adding the basic c_types as their own file section.

Also, added the to_c_string and from_c_string functions. Their
location needs to be determined.

src/c_types.rs

@@ -0,0 +1,70 @@
+//! This defines the primitive types that may be seen
+//! when creating 'C' bindings.
+//!
+//! There are several places where the target architecture and the OS
+//! require special consideration. These are handled
+//! with configuration statements.
+
+// Character types.
+#[cfg(any(target_os="android", target_os="emscripten",
+          all(target_os="linux",
+              any(target_arch="aarch64", target_arch="arm",
+                  target_arch="powerpc", target_arch="powerpc64"))))]
+pub type CChar = u8;
+
+#[cfg(not(any(target_os="android", target_os="emscripten",
+              all(target_os="linux",
+                  any(target_arch="aarch64", target_arch="arm",
+                      target_arch="powerpc", target_arch="powerpc64")))))]
+pub type CChar = i8;
+
+
+pub type CIChar = i8;
+pub type CUChar = u8;
+
+
+
+// Integer types.
+#[cfg(any(target_pointer_width="32", target_os="windows"))]
+pub type CLong = i32;
+
+#[cfg(any(target_pointer_width="32", target_os="windows"))]
+pub type CULong = u32;
+
+
+#[cfg(all(target_pointer_width="64", not(target_os="windows")))]
+pub type CLong = i32;
+
+#[cfg(all(target_pointer_width="64", not(target_os="windows")))]
+pub type CULong = u32;
+
+
+pub type CShort = i16;
+pub type CUShort = u16;
+pub type CInt = i32;
+pub type CUInt = u32;
+pub type CLongLong = u64;
+pub type CULongLong = u64;
+pub type CFloat = f32;
+pub type CDouble = f64;
+
+
+
+// Void types.
+/// To return void from a 'C' function it should return an empty tuple ().
+/// This type is just a descriptive version of that. **DO NOT** use this
+/// as an argument to a function. Use the c_void type for that.
+pub type CReturnVoid = ();
+
+/// This acts as a 'C' void pointer to pass to functions. **DO NOT**
+/// use this as a return type from a 'C' function. If a 'C' function
+/// returns void, then use the c_return_void type for that.
+#[repr(u8)]
+pub enum CVoid
+{
+   #[doc(hidden)]
+   _Variant,
+
+   #[doc(hidden)]
+   _Variant2
+}