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
 BestMoveChanges += (Signals.failedLowAtRoot + 1 )/2.;
BestMoveChanges += Signals.failedLowAtRoot;
 failedThisIterationLowAtRoot
shift by  failedThisIterationLowAtRoot , 0.9
cleaner, 0.93