few more docs

Hi,

although I might touch these sources again tomorrow, I thought it's good to open a PR in order to receive early feedback (mostly of crude type about missing pieces/paragraphs). Yet, any feedback is welcome :)

tia, F.
you dropped a significant part from this page that deals with porting from legacy configuration to the current configuration style, see https://github.com/hpcugent/easybuild/wiki/Configuration#legacy-configuration-deprecated .
Either point there, or include that part in a separate page.

This is particularly important since we'll be dropping support for the old config style in EasyBuild v2.0, tentatively planned for Jan'15, so it should be included in the documentation, so we can point to it from a page explaining the stuff that we broke in EasyBuild v2.0.