Initial sketch of --check flag.
Full spec of --check argument.
--check arg handles relative paths and throws exception for non-directory arg.
Added check for '@journal article' instead of '@article'.
Added check for errant eid field.
Added check for missing bibTeX key.
Added check for capital AND in author field.
Added check for UTF-8.
Added check for files that cause pybtex to throw an error.
Also parsing the files with pybtex, so I'll see any warnings.