Fix invalid parser's blocks patterns

[rafalp]

Adds test checking that block next to other block is parsed as two separate blocks, with extra logic for handling exceptions.

Also fixes lists parser because that one is very out of spec.

Fixes #1880

TODO

• Fix lists parser
• Fix tests other than blocks test
• Add missing blocks to the test matrix
  • Indented code
  • Quote
  • Table

[coveralls]

coverage: 97.164% (-0.009%) from 97.173%
when pulling 0dea95f on fix-1880-cleanup-linebreak-in-patterns
into 4d4b449 on main.