Various docstring tweaks. Fixed 'subst_vars()' so it actually blows up like the docstring claims   (and fixed the docstring not to claim it handles ${var}, which it   doesn't).
Various docstring tweaks.
Fixed 'subst_vars()' so it actually blows up like the docstring claims
  (and fixed the docstring not to claim it handles ${var}, which it
  doesn't).

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator