TWiki Reader: add new new twiki reader

This adds a reader for TWiki source files. It tries to parse the twiki source code as close as possible to the wiki but it only supports a few HTML tags (the wiki supports full HTML). Additional the wiki has an own macro language http://twiki.org/cgi-bin/view/TWiki/TWikiVariables#Parameterized_Variables_Macros. The parser also parses this but does not handle any semantic value. The macros only generate span elements with all the parameters included and the special class "twiki-macro" so that the user can transform this elements with custom filters afterwards.