Some overloaded operators of my own

So I had a chance to go and play around some with the operator 
overloading code today. Very nice work Stefano! To try things out 
(building off of your work with IntSets) I added some new functions / 
methods / and overloaded operators to Stringset (which reminds me I 
really should bite the bullet and rename that class from "Stringset" to 
"StringSet" ... ugh) .

Anyhow, I added support for the * and *= operators in your structure 
just so I could get a hang of how the whole process worked. Very nice 
overall! I had to alter mxc.l a little bit because the times operator 
was matching the C dereference operator so I added an extra lexical 
state for tokens that should only be matched in C prototypes vs moto 
prototypes. We should probably add the rest of the operators in now 
though just to make sure we aren't going to run into any other lexing / 
parsing bugs.

Here are the new methods I added, tests for them are in 
util_stringset.moto

-Dave

/** Add the contents of Stringset <i>s</i> to this Stringset. If a 
matching String
was already present it is replaces with <i>s</i> **/
void Stringset::addSet(Stringset s) =>
       void sset_addSet(Stringset *this, Stringset *p);

/** Clones the contents of this Stringset **/
tracked Stringset Stringset::clone() =>
       Stringset* sset_clone(Stringset *this);

/** Returns true if this Stringset contains the same elements as 
<i>S</i> **/
boolean Stringset::equals(Stringset s) =>
       int sset_equals(Stringset *this, Stringset* S);

/** Removes the contents of Stringset s that are contained in this 
Stringset **/
void Stringset::removeSet(Stringset s) =>
       void sset_removeSet(Stringset *this, Stringset *p);

/** Returns the union of two Stringsets **/
tracked Stringset Stringset::+=(Stringset i) =>
       Stringset * sset_union(Stringset *this, Stringset *i);

/** Returns the intersection of Stringset i1 and Stringset i2 **/
tracked Stringset Stringset::*=(Stringset i) =>
       Stringset * sset_intersection(Stringset *this, Stringset *i);

/** Returns the difference Stringset i1 and Stringset i2 **/
tracked Stringset Stringset::-=(Stringset i) =>
       Stringset * sset_difference(Stringset *this, Stringset *i);

/** Returns the union of two Stringsets - {x:x is in s1 or x is in s2 } 
**/
tracked Stringset +(Stringset s1, Stringset s2) =>
       Stringset * sset_union(Stringset * s1, Stringset * s2);

/** Returns the intersection of two Stringsets - {x:x is in s1 and x is 
in s2 } **/
tracked Stringset *(Stringset s1, Stringset s2) =>
       Stringset * sset_intersection(Stringset * s1, Stringset * s2);

/** Returns the difference Stringset i1 and Stringset i2 - {x:x is in 
s1, x is not in s2}  **/
tracked Stringset -(Stringset s1, Stringset s2) =>
       Stringset * sset_difference(Stringset * s1, Stringset * s2);

/** Returns the union of two Stringsets - {x:x is in s1 or x is in s2 } 
**/
tracked Stringset union(Stringset s1, Stringset s2) =>
       Stringset * sset_union(Stringset * s1, Stringset * s2);

/** Returns the intersection of two Stringsets - {x:x is in s1 and x is 
in s2 } **/
tracked Stringset intersection(Stringset s1, Stringset s2) =>
        Stringset * sset_intersection(Stringset * s1, Stringset * s2);

/** Returns the difference Stringset i1 and Stringset i2 - {x:x is in 
s1, x is not in s2}  **/
Stringset difference(Stringset s1, Stringset s2) =>
       Stringset * sset_difference(Stringset * s1, Stringset * s2);