Enhance Var.toUnicode to present uniquely-named variables a bit more readably.
Rename, move code related to Vars and generated names, for clarity.
Tweak styling.
Add utilities for tracking function calls.
Generation of bound vars now uses only the first letter of the original name,
to avoid multiple numeric parts.
Implement option for facts to be accepted without proof.
Turn off Toy.assertFacts by default.
Add TODO on variable naming.
Remove Expr.normalized and friends, which are unused and not helpful.
Comment.
Remove "Toy." qualifier from uses of Var in theorems.js.

--HG--
extra : amend_source : 6ab7475de6294553dfdaaacf32ada703492bf657
Remove unneeded instances of "Toy." in expr.js.
Define new function Toy.constify.
Replace occurrences of "new Var" with varify or constify.
Fix algebra1.html to work with updated APIs.
Extend Expr.isConst and Expr.isVariable to accept a name; add
Expr.isAtomic, extend isInfixDesired.
Remove occurrences of "Var" except in Expr.js and Expr method implementations
in other files.
Change Var to Atom throughout.  Independently, add "methodical" function
for classes.
Extended Toy.extends to set up the constructor "$" and "methods".
Removed "methodical" as superseded.
Add Expr.traverse method.
Make basic simplification facts available publicly.