Allow for default experation to be set globally

[mogorman]

I almost never want my memos to be permanent. this makes it easier to set that option globally rather than having to write it for every function.

[mogorman]

I made it compile time as I didn't want to put any performance changes as most people probably won't take advantage of it. the disadvantage of this approach is when variable is changed the dependency needs to be recompiled.

[melpon]

Supported https://github.com/melpon/memoize#cache-strategy---memoizecachestrategydefault