Simplify code by using NSCache for the time zone cache dictionary

[steipete]

This is similar to #38, but uses an NSCache, which allows us to delete even more code. It's slightly slower than using the plain NSDictionary, but the difference is 0.001 sec on my machine, and it doesn't measure the benefits of not having to register for memory warnings. I'd go for that one.

[ypresto]

I really want this PR to be merged, because it fixes thread-safety problem.
I have race condition (thread-safety) issue on v0.7.

Thread : Crashed: NSOperationQueue 0x1909cd80 :: NSOperation 0x191c9e10
0  CoreFoundation                 0x246eb138 -[__NSDictionaryM objectForKey:] + 195
1  CoreFoundation                 0x246eb0bd -[__NSDictionaryM objectForKey:] + 72
2  MayChannel                     0x001c0c27 -[ISO8601DateFormatter dateComponentsFromString:timeZone:range:fractionOfSecond:] (ISO8601DateFormatter.m:619)
3  MayChannel                     0x001c0f87 -[ISO8601DateFormatter dateFromString:timeZone:range:] (ISO8601DateFormatter.m:692)
4  MayChannel                     0x001c0f4b -[ISO8601DateFormatter dateFromString:timeZone:] (ISO8601DateFormatter.m:686)

Thread : NSOperationQueue 0x1909cd80 :: NSOperation 0x19026450
...
28 CoreFoundation                 0x24731039 -[__NSCFCalendar dateFromComponents:] + 1208
29 CoreFoundation                 0x24730ab5 -[_NSCopyOnWriteCalendarWrapper dateFromComponents:] + 148
30 MayChannel                     0x001c0fc9 -[ISO8601DateFormatter dateFromString:timeZone:range:] (ISO8601DateFormatter.m:701)
31 MayChannel                     0x001c0f4b -[ISO8601DateFormatter dateFromString:timeZone:] (ISO8601DateFormatter.m:686)

[steipete]

Oh wow, I had no idea this wasn't merged yet. Doesn't look like the repo is still maintained.

[ypresto]

Oh... Is this project abandoned? > @boredzo

[boredzo]

It's not abandoned; I just have a to-do graph a mile wide. This project has still has a place in it, though.

[boredzo]

Thank you!