My profiler shows that some remarkable % of CPU is spent on generating this string: (" " + c + " "). Now we check for CSS class without generating the new string. The code is longer, but faster.

Now we check the "lang" attribute without calling `String.split` method which generates new strings.

…er private final

in some places, I replaced them with `synchronizedMap()` or `ConcurrentHashMap`.
Not 100% sure nothing gets broken. :)
But at least all tests are still green.

I don't know what was the initial idea, and was it intended to pass any other parameters, but currently only `org.w3c.dom.Node` is passed there.

My profiler shows that `nsh.getClass((Element) e)` consumes quite a remarkable percentage of total CPU time.
So I hope caching these value could improve performance (though, my profiler doesn't show it :) ).