VideoSoftware: Optimisations: Promoted all s16s to s32's in TEV

Modern x86 processors are really bad at dealing with 16 bit types. On a
Core 2 cpu, any cache line containing a length changing prefix will have
a decode penalty of 6 cycles.

On Sandy bridge or later, each lenght changing prefix will add a 3
second penalty to decoding (and will be better on average).
VideoSoftware: Optimisations: Fixed some comments in Tev.cpp
VideoSoftware: Optimisations: Pass by Value instead of Refrence.

These bitfields fit in a single 32 bit registers and are not modified
inside the function. These functions are very hot, and the indirect load
had a measurable performance impact.

Also marked them as const, because they are.
VideoSoftware: Optimisations: Mark Aliasing pointers as const.

They don't change, and this allows the compiler to reason about them
better.

Also maked various fields as aligned; GCC's autovectorizer actually
manages to vectorize a small loop now.