PWG ls markup: handle 'unknown'

[funderburkjim]

This continues the markup improvements regarding literary sources in PWG dictionary.

There are about 2000 <ls>X</ls> identified as 'unknown' because:

• X does not start with a known tooltip abbreviation, and
• X does not start with a digit.

The changes here result in 0 unknown.

[funderburkjim]

Markup has been changed so that there are no more 'unknown' ls. Work is done in lsunknown directory.

• change_lsunknown.txt shows the changes in pwg lines of pwg.txt
• lsunknown_0.txt identifies the problematic ls items
• lsextract_pwg_0.txt shows the counts of different ls works, before correction.
• lsextract_pwg_2.txt shows the counts of different ls works, after correction.