Too short maximum length for externalpages.link

The script crashes as content.rdf now contains several links which are longer than the maximum 650 characters. I changed this value to allow 750 character links.
Merge branch 'patch-2' of https://github.com/siccovansas/dmoz2db into siccovansas-patch-2

Conflicts:
	src/lib/schemes/table_scheme.py
Merge branch 'siccovansas-patch-2'

Resolved conflict with pull request. Thanks siccovansas for patching!