Use the linker for selectors instead of the runtime

[mjbshaw]

This gets rid of runtime selector initialization. How it works is pretty straightforward:

Instead of calling objc_msgSend, we call objc_msgSend$SELECTOR, where SELECTOR is the selector we want to call. Two examples:

• To use the "description" selector on an object, we call objc_msgSend$description.
• To use the "setObject:forKey:" selector on an object, we call objc_msgSend$setObject:forKey:.

The linker then automatically patches these up to the correct selector. The value of the second argument to objc_msgSend (the selector) doesn't matter so this just passes undefined.

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[slimsag]

@mjbshaw some merge-conflicts from your other PR to address

[mjbshaw]

@slimsag Resolved. I guess I should abandon my fight against GitHub and trying to do one-commit-per-PR. I'll batch the next PR so it has multiple commits.

[slimsag]

@mjbshaw multiple commits per PR is totally fine, especially when changes are as solid as the ones you are making so far :)