1.2.0 (<insert date>)
* Added a structure<T> template class for the easy creation of user-defined
algebraic classes.
+* Improved the speed of subs() and normal() by the use of maps instead of
+ lists.
* Many internal reorganizations and optimizations.
* Caveats for class implementors:
- basic::copy() and basic::destroy() are gone; classes derived from
basic can use the defaults for the assignment operator and copy
constructor.
+ - basic::subs() and basic::normal() take an 'exmap &' instead of two
+ 'lst &'.
- basic::subs() now descends into subexpressions (if accessible via
nops()/op()/let_op()). If you have a custom implementation of subs()
that calls basic::subs() after substituting subexpressions, this needs