Merge pull request #156 from getcwd/master

Update caching framework document to include LRU
Fix set-placeholder definition.
Merge pull request #157 from comel/patch-1

Fix set-placeholder definition.
Updated the examples, added hints and clarity.

Thanks for adding the perl uwsgi::spooler function
Spooler == awesome.
Merge pull request #158 from brianhorakh/patch-2

Updated the examples, added hints and clarity.
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