Problem:    The libvterm code is outdated.
Solution:   Include libvterm changes from revision 802 to 817.  Revert some
            changes made for C89.

Problem:    The libvterm code is outdated.
Solution:   Include libvterm changes from revision 790 to 801.

Problem:    Various comment problems.
Solution:   Update comments.

Problem:    Libvterm code lags behind the upstream version.
Solution:   Include revision 719.

Problem:    Libvterm code lags behind master.
Solution:   Sync to head, solve merge problems.

Problem:    Libvterm can be improved.
Solution:   Various small improvements, more comments.

Problem:    No terminal emulator support.  Cannot properly run commands in the
            GUI.  Cannot run a job interactively with an ssh connection.
Solution:   Very early implementation of the :terminal command.  Includes
            libvterm converted to ANSI C.  Many parts still missing.