* Add some new expression functions and macros.
See misc/math-expr.md for the list of added functions, except for
"like", which previously existed but was not documented.
* Add easymock to datasketches tests.
* Add easymock to distinctcount tests.
* Add easymock to virtual-columns tests.
* Code review comments.
* Clean up code a bit.
* Add easymock to scan-query tests.
* Rework ExprMacros that have multiple impls.
* Improve test coverage.