Update documentation to follow table structure

[Relequestual]

After taking a look at the Beacon Project protocol draft, I think the documentation found in this repo should be updated so that object properties are easier to read.

Using a table structure with the headings "Property, Required, Value, Description" results in documentation that as far easier to read. Any objects can be further defined and linked to, for example a Patient.

[sdumitriu]

Hopefully the whole table will fit in the small width that GitHub provides for the content.

[buske]

@Relequestual I hope you like the table in the manuscript. :)

[Relequestual]

I'd like to pick this task up, as it overlaps with some work I'll be doing in a few months time. Although happy for someone else to pick it up before I do, so I won't claim it.