Update documentation

[erikbosch]

• Clarifies string/float/double.
• Reformat recommendations to state that they also are rules for VSS catalog
• Remove enum recommendation

Proposed follow-up actions if PR accepted.

• Remove enum name check from vss-tools (So that for example no warning is given for Vehicle.OBD.PidsA)
• Add a "case insensitive uniqeness check" for VSS name so it give error in strict mode if you have both Vehicle.Cabin.Abc and Vehicle.Cabin.ABC
• When done adapt Makefile used in CI so that we enforce recommendations for the standard catalog.

Fixes #705 Fixes #706 Partially #700 (but more needed to complete it) Fixes #662 Fixes #280

[erikbosch]

MoM: Please review

[erikbosch]

PR updated to address comments

[erikbosch]

MoM: Merge