Define sorted insertion macro.
Implement hidden question database

Also improve read question code.
Hidden question functionality implemented in the question list
Merge branch 'master' into hidden-questions
Provide cache invalidation

(sx-cache--invalidate): Invalidate provided cache.  Allows for
invalidating variables associated with cache using `makunbound`.  Cache
can be reinitialized using arg `init-method`.
(sx-cache-invalidate-all): Invalidate all caches then call
`sx-initialize` to reinitialize.  Arg `save-auth` prevents access_token
from being lost.
Fix docstring.
Use `cl-remove-if` rather than `remove-if`
Merge pull request #73 from jleechpe/invalidate-cache

Provide cache invalidation
Merge pull request #71 from vermiculus/hidden-questions

Hidden questions
Mark as read with "m"

Fixes #61
Merge pull request #76 from vermiculus/mark-read-key

Mark as read with "m"
Add some package definitions.

Also run checkdoc on sx.el
Fix missing dependency