This adds a new function to create a preparsing input thread, and
runs preparsing within a dedicated thread.

std::max is only defined on same T type. Older GCC fail to promote it
correctly.

because we'll need fake chunks

for WMV/VC1

and fix write overflows

should be reusable

Timeline was only supposed for live usage

still carried from early impl

Previously, when Close() was called, SPU region were not properly cleared.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>