LibWeb: Start building the tree building part of the new HTML parser

This patch adds a new HTMLDocumentParser class. It keeps a tokenizer
object internally and feeds itself with one token at a time from it.

The names and idioms in this class are expressed as closely to the
actual HTML parsing spec as possible, to make development as easy
and bug free as possible. :^)

This is going to become pretty large, but it's pretty cool!

Libraries/LibWeb/CMakeLists.txt

@@ -84,7 +84,9 @@ set(SOURCES
     Layout/LineBox.cpp
     Layout/LineBoxFragment.cpp
     Parser/CSSParser.cpp
+    Parser/HTMLDocumentParser.cpp
     Parser/HTMLParser.cpp
+    Parser/HTMLToken.cpp
     Parser/HTMLTokenizer.cpp
     ResourceLoader.cpp
     StylePropertiesModel.cpp