(r2b-convert-record, r2b-convert-buffer): Improve argument/docstring

(r2b-convert-record, r2b-convert-buffer): Improve argument/docstring
consistency.  Doc fixes.
(r2b-variables, r2bv-address, r2bv-annote, r2bv-author,r2bv-booktitle,
r2bv-date, r2bv-decade, r2bv-editor,r2bv-entry-kind, r2bv-institution,
r2bv-journal, r2bv-keywords,r2bv-kn, r2bv-month, r2bv-note, r2bv-number,
r2bv-ordering,r2bv-organization, r2bv-pages, r2bv-primary-author,r2bv-publisher,
r2bv-school, r2bv-title, r2bv-title-first-word, r2bv-tr, r2bv-type, r2bv-volume,
r2bv-where, r2bv-year): Defvar at compile time.