Dot

[leissa]

New dot emitter

• does not depend on Emitter class or any other fancy analyses and should work even with (partially) broken Thorin programs
• colored nodes
• tooltips show additional infos
• hidden edges for things like edges to Lits or backedges from var -> mut
• Within gdb simply do this to visualize a Def:

  (gdb) xdot def

• docs (see coding.md for details on xdot/gdb stuff)
• removed old dot emitter