Removed unnecessary type 'key'

	modified:   ocaml/feature_table.ml
Then array representing the argument names is always consistent

By entering a proof context it is never possible that the array
representing the argument names is empty and then variable 'nbenv'
is different from zero.

	modified:   ocaml/proof_table.ml
Added function and variable renaming

- Added the function 'push_empty' to push a context without any
  new variables.

- The variable 'c' is used consistently to describe the context and
  not 'loc' as previously.

	modified:   ocaml/context.ml
	modified:   ocaml/context.mli
Corrected printing of quantified terms

	modified:   ocaml/feature_table.ml
	modified:   ocaml/support.ml