Upgrades dox to Doxyfile version 1.8.3

Upgrade removes deprecated options HTML_ALIGN_MEMBERS, SHOW_DIRECTORIES and USE_INLINE_TREES. These are deprecated since Doxygen release 1.8.1 (2012-05-09) [http://www.stack.nl/~dimitri/doxygen/changelog.html#1.8.1].
Sets readme.md to be used as MainPage for generated documentation
Moves example documentation from xmltest.h to xmltest.cpp
Merge pull request #91 from martinsh-shaiters/doxyfix

Example documentation moved to xmltest.cpp