Definitions section

[heidivanparys]

Some minor things about the definitions section

• change link to ISO definitions to the term itself, not just the standard (e.g. https://www.iso.org/obp/ui/#iso:std:iso:19118:ed-2:v1:en:term:4.13 instead of https://www.iso.org/standard/44212.html)
• if at some point an agreement is reached on "dataset", that definition should be updated, see opengeospatial/ogcapi-features#312
• update the definition of content negotiation to "practice of providing multiple representations available via the same URI". See also https://www.iso.org/obp/ui/#iso:std:iso-iec:19788:-7:ed-1:v1:en:term:3.4 and https://www.w3.org/TR/2004/REC-webarch-20041215/ for notes and source.