Add missing standard library includes for self-sufficient headers

Fixes builds with newer GCC/libstdc++ that no longer provide <cstdint>,
<cstring>, <cfloat>, <memory>, <algorithm> etc. transitively. Also
disambiguates visit<> calls in taxonomy.h with the full namespace and
casts the character value in IfcCharacterDecoder to uint32_t to silence
ambiguous overload warnings.

src/ifcparse/instance_data.h

@@ -37,6 +37,11 @@
 
 #endif
 
+#include <cstdint>
+#include <cstring>
+
+#include <boost/optional.hpp>
+#include <boost/shared_ptr.hpp>
 #include <boost/logic/tribool.hpp>
 #include <boost/dynamic_bitset.hpp>