Use freeArray in HashMap destructor

This ensures destructors are called on the elements in the hash map. I'm not sure if this fixes anything but it seemed like it could have caused issues eventually.
Added basic redis documentation pulled from redis.io
Fix ExampleSerializer example
Merge pull request #897 from Marenz/patch-1

Fix ExampleSerializer example
Merge pull request #894 from etcimon/redis-documentation

Added basic redis documentation pulled from redis.io
Merge pull request #893 from etcimon/patch-1

Use freeArray in HashMap destructor
Update change log.
Add structure to the 0.7.21 feature list.
Fix typos.