Installed Indeterminates for fields.
New doc style.
Remove compatibility code for GAP 4.4

This fixes a conflict with "gap -O", as the "VERSION" variable
is deprecated in GAP these days.
fixup: add back extra AddToMatElm declaration
Merge branch 'master' of https://github.com/sebasguts/MatricesForHomalg into sebasguts-master

* 'master' of https://github.com/sebasguts/MatricesForHomalg:
  New doc style.
  Installed Indeterminates for fields.