Process character references in data

[mina86]

Re-escape characters in data to minimise code further. In data sections only ampersand and less-than sign need to be escaped. Since characters are always shorter than their entities not escaping what doesn’t need to saves space. Furthermore, don’t escape ampersand in situations in which HTML5 dictates it doesn’t need to be escape.

[mankyd]

Thanks for the PR. I am going to spend some time digesting this and hope to get it in soon if it makes sense.