Fix compile for some versions of mingw

The bswap intrinsics are specific to the compiler, not the
host platform.

No functional change.

Resolves #155
Coding style in TT code

In particular seems more natural to return
bool and TTEntry on the same line, actually
we should pass and return them as a pair,
but due to limitations of C++ and not wanting
to use std::pair this can be an acceptable
compromise.

No functional change.

Resolves #157
Improve comments in UCI

And simplify naming while there.

No functional change.

Resolves #159