Reorganise TOC

[Joseph-Edwards]

This PR moves some files around so that:

• there is a "Package Info" with authors, biblio, installation and changelog;
• there is a "Core classes" section for Runner and Reporter and ReportGuard;
• there is a section for constants, that has been corrected to remove references to hidden types;
• there is an enum page that documents all module level enums.

The enum doc still need to be normalised, but this will be done in a later PR.

[james-d-mitchell]

Sweet thanks @Joseph-Edwards