Added HTML support. We still had a lot of issues when running xml2.0
files (we made it out to work only with 2.0_bis ones, because we
anticipated stores to always get robbed). Either way, it's working now.
Output now works through an OutputObject. This way we can implement HTML
output and regular output together. We still need to refine the HTML
matrix output a bit more. As I said before there is a new object
OutputObject (.cpp/.h) which is a data member of City and which will
handle our output. We also have 2 new files: helpers.cpp/helpers.h which
contains functions like intToString() and doubleToString().