Rudder

rudderlang had only blocking errors, stopping at the first error encountered. Plus, context of errors where often not right (either too large or off the error line)

This PR offers a more precise error context passed to errors.
It also integrates a parser function to throw non blocking errors, that become failure only if no scope-relative parser succeeds.
The first error met in its parent scope is returned, as following code cannot be reliably parsed since it depends on an error