TagHelpers: Create parse visitors that understand "special" html

[NTaylorMullen]

We'll create visitors that will run through the syntax tree to then re-construct a tree that understands the "special" html that's dictated by #70.

Pre-requisites: #72, #70

[NTaylorMullen]

This needs to also handle "VoidElements"

[yishaigalatzer]

duplicate of #69

[NTaylorMullen]

Not dup. 69 was the dup of 72