Documenting tcl files

Next: Documenting application specific files  Prev: Documenting flex files

TCL is not a structured language, so I find only two elements worth documenting, proc and set. TCL auto comment is `##'.

For example

## Documentation for f.
#  More on f.
proc f {args} {
  ...
}

## Documentation for v.
set v ...

## Documentation for a.
set a(...) ...