urllib2 is renamed and reworked in Python 3, handle this change by
importing urlopen and HTTPError directly.
Resolve the print issues, by using print() everywhere.
Python3 reads bytes when reading from urlopen() therefore convert it to
a string with .decode('utf-8')
- Using a separate build directory currently fails during make install
because none of the files under doc/holidays or doc/themes are being
by cmake into the build dir. Add CMakeLists.txt files for both
doc/holidays and doc/themes, and add the corresponding add_subdirectory
directives to doc/CMakeLists.txt, to ensure these files are always
copied into the build directory and installed correctly.
