Fetches a JSON file containing information about all namespace
names and aliases across all wikis using action=sitematrix and
action=query&meta=siteinfo. This file is used later by
`aggregate` to parse page names into (namespace, title)
pairs.
Usage:
fetch_global_namespaces (-h|--help)
fetch_global_namespaces <api-host>
Options:
-h --help Prints this documentation
<api-host> URL for the MediaWiki host to query for
action=sitematrix
