EnableCXX11, abort if cannot find suitable C++11 compiler
Fixed wrong include
Fix test execution order

test_hog_bow requires a dictionary files so must run after
test_vocabulary which actually saves a vocabulary to file.
Of course test dependencies should be avoided ...
Added build instructions to README
Moved all includes to vis/ and ordered include directives

All header in libvis are under subdirectory vis to reflect also the
underlying namespace.
Moreover, includes are ordered in such a way that local headers are
included first, then 3rd party libraries and than the Standard Library.
Added named default progress handler
Added sample handlers in vis/utils/handlers.hpp

Currently the only supported handler just print the name of the current
file being processed.
Added progress handlers to demo application