Clarify spec details in KHR_audio and add property summary tables

[aaronfranke]

Syncing with omigroup/gltf-extensions#199

Several aspects of the spec were not clear before. Changes:

• Add property summary tables for all properties.
• Specify default values in the tables and the prose.
• Add details on the cone angle, specify this is an angular diameter and not a radius (this matches Web Audio).
• Add note that a max distance of 0 should be treated as an infinite max distance.
• Remove limitation of max distance only being available on linear, allow it for all.
• Update the cone diagram to be clearer.

[antpb]

We've gone through this line by line as a group and independently. LGTM!