Initial work to create dokuwiki writer (#386)

In this first version, all dokuwiki files are straight copies of the
media wiki counterparts.
Implemented correct output of dokuwiki (#386)
Implemented Emphasis (italic) and Strong (bold) for dokuwiki (#386)
Implemented horizontal rule for dokuwiki (#386)
Weak implementation of hyperlinks for dokuwiki (#386)

TODO Simplify the code
Implement conversion of images in dokuwiki writer (#386)
Add failing test for bullet and numbered lists in dokuwiki writer (#386)
Corrected part of the failing test for lists in dokuwiki writer (#386)
Convert bullet and numbered lists in dokuwiki writer (#386)
Added some todos to dokuwiki writer (#386)
Added another todo -  dokuwiki writer (#386)
Implemented linebreaks in dokuwiki writer (#386)
Removed incorrect entity conversion in dokuwiki writer (#386)
Implement footnotes in dokuwiki writer (#386)
Implement strikeout in dokuwiki writer (#386)
Initial implementation of tables in dokuwiki writer (#386)

Todo: alignment, and headings
Implement table headings in dokuwiki writer (#386)
Implement <code> blocks in dokuwiki writer (#386)
Don't add entities in <code> blocks in dokuwiki writer (#386)
Fixed inlined code in dokuwiki writer (#386)