[doc] Respect platforms field in doc generator
[doc] Respect platforms field in doc generator

When a member definition in a API JSON file has a platforms object, 
add span elements describing which platforms support this member to 
the generated header. The elements have specific CSS classes making it
possible to style these in HTML.

Change-Id: I9513807038b0c31afaa8bfd20f7bba768c997b8a

eclipsesource/tabris-js,eclipsesource/tabris-js,eclipsesource/tabris-js