Rename sx-network to sx-site

According to the documentation, it's the appropriate terminology.
Merge branch 'master' into network-list

Conflicts:
	sx-site.el
Use narrow filter for site list
Merge branch 'master' into network-list
Move question sorting function to sx.el

It is not specific to questions -- it is generally applicable to any
alist.
Don't need to hexify filter
Include more fields in the sites filter
Add favorite sites customization
Convenience argument for `cache-get'

Allows for setting the cache if it does not exist.
Use smart caching
Merge branch 'master' into network-list

Conflicts:
	sx-filter.el
	sx-question.el
Fix comment
Merge pull request #53 from vermiculus/network-list

Smart caching