Locations not properly updated when parsing multi-line block strings

[ErikWittern]

Currently, the parser considers multi-line block strings wrongly to be placed in a single long line. For example, this block string is considered to have the location:

{"start": {"line": 49,"column":56}, "end": {"line":49,"column":96}}"

...whereas it should end in line 53, column 6. Subsequent locations are correspondingly off by a few lines.