GXemul Code2

Enabling -Werror again; seems to work on my machine for clang and most GNU C++ versions (up to 9).

bootblock.cc now parses SGI disk boot blocks, and tries to load the OSLoader (sash), if booting without an explicitly provided OS kernel.

Slightly nicer indentation for ARC/ARCS boot info.

Reshuffling the TODO.

Adding support for masks for memory mapped components in the new framework. Used so far by the HP 700/RX, which has 2 MB RAM repeated throughout 0x30000000..0x3fffffff.

Message when trying to disassemble too far.

Fix crash for short output.

Minor update.

Copyright year update.

Applying a rather large patch from Jason Thorpe for using /dev/tap devices in addition to the existing networking modes. The patch also consists of enhancements to the DEC21143 and Lance ethernet devices to perform packet filtering.