Rearrange some code, work on comments.
More work on comments.
Add Expr.visitCalls and test.
Remove one test that exists to produce an execution profile.
Add rules.simplifyMath1; convert reversePath to Path.reverse().
Modify StepEditor.tryRule to do as many trivial simplifications
as it finds after running any particular step.
Fix one test.

--HG--
extra : amend_source : e41c48cd3ba65b1e8d7a6373eedd341b272034d3
By default do not show rules.simplifyMath1 in the rules menu,
as it is done automatically and the result can look odd when
it does not apply.