Features

Added support for count(*) in expressions. Produces the same result as count().
Added explicit checks for
- Query before execution: checks for structural integrity, non-existing calculations/transforms, transform argument types etc.
- Model just after parsing: checks for structural integrity, that fields like time don't reference non-existing calculations, that related tables' related_key is set up correctly
- Model after the actual model instantiation: checks for referenced calculations — which calculations are allowed where, circular refs
Added sensible custom exceptions for the checks
Added nicer syntax errors for expressions and shorthand definitions
Changed the syntax for custom properties in shorthand definitions, now it requires { }:
%metric invoice_items.revenue = sum(Quantity * UnitPrice) { format=currency }

Bug fixes

Fixed field generation for x2, y2 Altair encoding channels. Before the fix, the integration tried to generate a timeUnit field, which is not supported by these channels (only field is supported)
Fixed derivative measures not respecting filters on child measures. Now measures are only allowed to reference non-filtered measures. Filtered measures are allowed in metrics.