Update dense hex serialization: use parenthesis rather than square brackets

parens are guarranteed to to be in a word due to the regex for a word.  This is a more robust guarantee that the guarrantee that all square brackets are stripped by the wiki stripper, particularly since some aren't and since this makes usage of other data sources hard.
Also update ReadableSerialization to use parens
Refactor: remove readable serialization, just use normal serialization with newlines.

--HG--
rename : A-vs-An/WikipediaAvsAnTrieExtractor/DenseHexExtension.cs => A-vs-An/A-vs-An-DotNet/Internals/NodeSerializer.cs
Use new serialization methods in linqpad test.
Fixup wikioutput-> dict  converter to use new API.