Data conversion functions assume little-endian architecture

While I don't have a big-endian platform for testing, it looks like rusha won't work correctly there. Reason is: the `switch (om)` and `switch(lm)` blocks in functions like `convBuf()` reverse byte order - assuming little-endian architecture. Most other places such as `getRawDigest()` function for example seem to work independently of platform's architecture.
