Draft: pass the buffer size to the bit readers

Similar code as featured in !22 but on top of !28.

Also requires libdvdnav!25

The code found in !22 already cannot overflow but the bitreader can be used with external buffers.

Given the PCI and DSI have fixed sizes we could also force the reader to use that size, since we are changing the API...

Draft until !28 is merged.