jquery.tablesorter: Minor coding style cleanup and DRY
* Consistently name 'length' cached variables 'len' (e.g. not 'l').
* Fix invalid documentation syntax for convertSortList().
(Build is passing because this file is not yet indexed.)
* Remove redundant 'len' variable from pure JavaScript arrays where
iterations can't change the length. Caching the length is a dated
practice meant to micro-optimise execution time. For the moment,
kept any loops with complex iteration bodies as-is, as well as loops
over structures that are not pure arrays (e.g. NodeList objects).
* Use getParserById() in addParser() instead of duplicating its logic.
Change-Id: I566eff6efd97b5d9672277bacb4cb2b501f4625f