New node formats

Additional support for BSP tree formats:

• ZDoom extended nodes
• ZDoom GL nodes (GLN segs)
• ZDoom GL nodes (GL3 nodes)

This is in practice a requirement for UDMF as ZDBSP will only build in these formats for textmaps.

Test files:

• srb2win-nodes.exe
• MAP10FUCK.wad
• SHITFUCK.wad