Guide macros and unsafe

The last two sections of the guide, and a small conclusion. I suck at conclusions.

I also realized I never covered strings, so I'm going to put that section up before we're actually 'done.'
There isn't currently. I tend not to talk about 'negative features,' but you are right. I think this information belongs in the macros guide though. Remember that these last two sections are supposed to be the briefest of introductions to these topics.