Fix hashsize() should return size_t.
Fix hashsize() should return size_t.

bstarynk/jansson,markalanj/jansson,akheron/jansson,Mephistophiles/jansson,akheron/jansson,bstarynk/jansson,Mephistophiles/jansson,markalanj/jansson,akheron/jansson,bstarynk/jansson,markalanj/jansson