Cleanup and utilities for interactive exploration

bug fix in cite_articles; better plot titles; basic topic and doc info
in more minimalist versions than the old ones in topics.R
improvements in some comments
readme update

with fix to tm_wide defaults so that example code in the readme works!

also: usage comment on tm_wide function; some tweaks in the metadata.R url
functions; and some primitive utility functions for interconverting
between the vanilla term-document matrix and the tm text mining
package's data types.