parse.go: Remove uneeded addition infoTextLen
parse.go: Reorder case statements
parse.go: Start error lines on the first item

For errors involving section titles, the reported line number in the system
message was being reported as the problem occurring on the title underline.
This parser is configured to use the line of the first item in the problem
section as the reported line number.
parse_test.go: Improve error output formatting
Add test TestParseSectionLevelBad0000

Forgot to implement the passing parser test for TestLexSectionLevelBad0000.
Add test LevelBad0001

Tests for bad section level ordering with title overlines.