Ignore &nbsp; in string
Do not fire same check on email address (issue #280).
Ignore ISBN keyword
Do not fire same check on URLs (issue #280)
Skip IRC channel from checking same strings (issue #280)
Skip domain names when checking for same string (issue #280)
Wrap too long lines
Cache same check results

The source string is most likely to be same in all languages so it is
useful to store ignore list in cache.