Override `non_shake_case' warning on per-function basis

This change removes global override of `non_shake_case' warning and replaces it
with per-function overrrides. This way, compiler will complain about style
guide violation in new code.

It should be noted, that `rustc' is not smart enough to emit warning when
override is no longer needed, it must be checked manually.

src/lib.rs

@@ -1,8 +1,6 @@
 #![allow(
     non_camel_case_types,
-    non_snake_case,
     non_camel_case_types,
-    non_snake_case
 )]
 #![feature(c_variadic, ptr_wrapping_offset_from)]