Add links from Hazard Data Package specification to the code lists

[ldodds]

The current draft of the Hazard Data Package indicates that some properties have their valid values defined by some code lists.

Once #11 has been completed, e.g. via #12, then the specification should be updated to link directly to the relevant code lists.

The code lists are all referenced as "RDL .... Code list" in the text.

[matamadio]

Code list for hazard being updated / under review

#2

[stufraser1]

superceded by defining new external codelists in current updates