A backend for the Sass cache using in-process memory.
If we deserialize this class, just make a new empty one.
@private
Create a new, empty cache store.
Since the {Memory} store is stored in the Sass tree‘s options hash, when the options get serialized as part of serializing the tree, you get crazy exponential growth in the size of the cached objects unless you don‘t dump the cache.
Destructively clear the cache.
@see Base#retrieve
@see Base#store
[Validate]