[API] Incorrect use of “representation”

[RubenVerborgh]

The API documentation describes subjects as "Subjects are representations of a subject".
This is terminologically incorrect; subject are subjects, not representations; i.e., http://example.org/subjects/Mathematics identifies the concept of maths, not a representation of the concept.

A correct (and less tautological) way to describe things would be "A subject is a branch of knowledge studied or taught in an educational institution". Similar for other properties.

[jhoobergs]

Indeed, I changed this from something else and now it doesn't really mean anything anymore. I'll fix it.