* lmc.el: Add a few more commands, and a tool-bar.

* lmc.el: Add a few more commands, and a tool-bar.
(lmc--assemble): Warn of duplicate labels.
(lmc-disassemble-word): Fix typo.
(lmc-mode-map, lmc-menu): Add bindings for run, set-pc, and set-acc.
(lmc-tool-bar-map): New var.
(lmc-mode); Use it.  Make the PC and Acc editable with a click.
(lmc-set-pc, lmc-set-acc, lmc-run): New commands.
(lmc-step): Update tool-bar after hitting HLT.
(lmc-asm-indent-line): Parenthesize if needed.