Introduce clang-format

An automated and opinionated style for code. We can decide to change the
style and have the source updated by the clang-format tool by running:

    make format

I've based the style on the Google style with exceptions to better
match
the current source style.

Change-Id: I43f85c7d4ce02ca999805558b25fcab2e43859c6
diff --git a/inc/std.h b/inc/std.h
index 7c10200..d7cc124 100644
--- a/inc/std.h
+++ b/inc/std.h
@@ -48,10 +48,11 @@
 #define htole32(v) __builtin_bswap32(v)
 #define htole64(v) __builtin_bswap64(v)
 
-#else /* __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__ && __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__ */
+#else /* __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__ && \
+	 __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__ */
 
 #error "Unsupported byte order"
 
 #endif
 
-#endif  /* STD_H */
+#endif /* STD_H */