Allow multi-line help comments in user defined VeLa functions

[dbenn]

Right now we can have:

<<This function squares its argument.>>
sqr(n:real):real{n*n}

We would like to allow this:

<<This function squares its argument
     but this time with integers.>>
sqr(n:integer):integer{n*n}

or

<<This function squares its argument>>
 << but this time with integers.>>
sqr(n:integer):integer{n*n}