Reorganise source files for the WinQuake project

Shift source files (extensions of '.c' or '.s') from 'WinQuake' to
'WinQuake\Src', and shift header files (extension '.h') from 'WinQuake'
to 'WinQuake\Include'.

Between the numerous Quake releases several distinct projects exist;
despite the source being intertwined. Separating build mechanisms from
source code (as opposed to all files existing in the same directory) is
an attempt to clarify this state.