Align marble string in Error message with spaces

[xuanswe]

Current error message:

Error: 
    "Source:   -(bbb)|"
    "Expected: (aaa)(bbb)|"

Expected error message:

Error: 
    "Source:   -    (bbb)|"
    "Expected: (aaa)(bbb)|"

I think the same frame of 2 streams should be aligned.

[kwonoj]

For this reason sandbox accepts spaces between marble tokens to align explicitly. It may possible to align automatically, but requires several edge case handling also violates assertion modifies source marble otself. Will think about feasibility in a long run.