Treetop rules for optional and mandatory spaces (thanks Clifford Heath)

Treetop optional and mandatory spaces

rule s # Optional space
  S?
end

rule S # Mandatory space
  (white / comment_to_eol / comment_c_style)+
end

rule white
  [ \t\n\r]+
end

rule comment_to_eol
  '//' (!"\n" .)+
end

rule comment_c_style
  '/*' (!'*/' . )* '*/'
end