Implement `first parse error` strategy to find error. I.e. find furthest matched `pos` in `input`

Implement simple debugging tracing
Move `calculators` examples to another namespace
Fix `error reporting` tests spec
Move error collecting from `ErrorUtils` to `Parser`

Make `nextChar` to track only cursor. Implement restoring line and column of error only during error formatting

Move `OpTreeContext` to upper package
Improve errors reporting to produce error stack frames
Implement `CharacterClass` operator (i.e. rule { "0" - "9" })