1.2.8

• Convert to use newer xdis (which handles 3.10)
• sphinx doc updates
• Generalize subcmdmgr for use in trepan-xpy trepan-xpy has a new class of subcommands Vmstack.
  So we need to be able to allow it to set trepanxpy as a base directory to look for
  subcommands in.
• Disassembly tweak: Show argval when there is one and argrepr == ''