improve error handling with line / position number

[nitram509]

Motivation

We should ensure that error messages produced are meaningful and easy to understand.
Every error message should not only contain the actual error, but also a line or position number to understand where exactly the error occurred - e.g. position 37, type mismatch, expected 'string'

Here are some sense checks

• are messages readable?
• do they contain a line number and column-position number?
• are users guided how to solve the issue?
• are tests in place to showcase error messages?
• is it easy to navigate from an error message to the root cause? (from developer perspective)

HINT: this issue relates to #17 ... we know some error messages already contain line/position number ... so this issue here is to ensure this is always the case (e.g. NewErrBadOp does not contain position information)