Merge: Improve lib/html and nitlight

Various improprement in the whole nitlight chain.

Before: nitlight --keep-going -d tmp ../lib/ ../src
* Elapsed (wall clock) time: 28.71
* User time (seconds): 47.25
* System time (seconds): 1.05
* Maximum resident set size (Gbytes): 2.1311

After: nitlight --keep-going -d tmp ../lib/ ../src
* Elapsed (wall clock) time: 22.97 (-20%)
* User time (seconds): 34.42  (-27%)
* System time (seconds): 1.06
* Maximum resident set size (Gbytes): 1.8924 (-11%)

After + new option: nitlight --keep-going -d tmp ../lib/ ../src --no-infobox
* Elapsed (wall clock) time: 10.71 (-63%)
* User time (seconds): 14.49 (-69%)
* System time (seconds): 0.83
* Maximum resident set size (Gbytes): 1.6713 (-20%)

Pull-Request: #2618