More progress on NewParser.
Removed Elements from Element.

It was entirely unnecessary, used only once (and dispensibly) in
Text.CSL.Eval.  This cleans up the code a bit.
Version bump to 0.6.
Simplified Choose.

Instead of taking an "if" and zero or more "if-elses", it just takes
a list of IfThen conditions.

This simplifies some of the logic.
Revert "Simplified Choose."

This reverts commit b04d9abab0936bbc1284fd92b6d9bb678ee7bbc7.

Thought better of it.  The original was better, since it
reflects that there must always be an if clause.
NewParser:  preliminary handling of choose.

message for your changes.  Lines starting
Small code readability improvement.
More work on NewParser.
NewParser: support number, label elements.
More progress on NewParser.
More on NewParser.
NewParser: support names element.
More progress on NewParser.
More NewParser improvements.
More fixes to NewParser.
More improvements to NewParser.
NewParser:  csMacros now matches the old parser.
Use $/ in NewParser.
NewParser:  Scaffolding for citation, bibliography elts.