Enhancement of @doc strings in rascal-core code

[jurgenvinju]

Is your feature request related to a problem? Please describe.

With the new @synopsis, @description tags the tutor is able to generate clearer layout with fewer unchecked textual idioms.

Proposal to rewrite all examples like this:

@doc{
.Synopsis
Compose two grammars.

.Description
Compose two grammars by adding the rules of g2 to the rules of g1.
The start symbols of g1 will be the start symbols of the resulting grammar.
}

to

@synopsis{Compose two grammars}
@description{
  Compose two grammars by adding the rules of g2 to the rules of g1.
  The start symbols of g1 will be the start symbols of the resulting grammar.
}

We have automated scripts for this in store in lang/rascal/tutor/conversions which were tested and executed on the standard library.