nsf.bst: import Jonathan Irwin's NSF template

Dated 2012 Oct 29 on his website. https://www.cfa.harvard.edu/~jirwin/tex/nsf.bst.
yansf.bst: preliminary tidying
yahapj.bst: add 'isbn' as a field, keying off of yansf

Not used, but might as well list it.
yansf.bst: more tidying; use URLs with my bibtex conventions
yansf.bst: don't munge title cases