Don't require proxies for a correct working

[mweststrate]

Fixes #8

First implementation is promising and feature complete! Needs some clean up, feature detection etc. Performance is quite neat so far (but bare in mind that the Proxy impl is not yet optimized, while the non-proxy impl is)

The update-10k-todos-in-a-set-of-100K benchmark:

    ✓ just mutate (2ms)
    ✓ deepclone, then mutate (475ms)
    ✓ handcrafted reducer (15ms)
    ✓ immutableJS (65ms)
    ✓ immer - with autofreeze (309ms)    // Immer, with auto freeze enabled
    ✓ immer - without autofreeze (148ms) // Immer, but without auto freeze enabled
    ✓ immer - NO PROXIES - with autofreeze (470ms)
    ✓ immer - NO PROXIES - without autofreeze (428ms)

[benbraou]

I don't see where isObject is used. Is this a typo?

[mweststrate]

yeah. auto import :(

[benbraou]

Great! 👏
I did not look thoroughly at the implementation details tbh. (I will do it this weekend, but this is independent from this PR of course. For learning purposes 😁)

[mweststrate]

@benbraou sorry, forgot to mark it as WIP! Still making some improvements besides the build :)