Documentation

I've taken a pass at updating the comments in the .h files. My intent was multifold:

- simply make the header files are a little more self-descriptive/self-documenting;

- you can generate reference documentation (see example at [http://robertmryan.github.io/fmdb/](http://robertmryan.github.io/fmdb/)) that looks more like Apple's documentation; I generated that help documentation using the following command line:

        appledoc --project-name FMDB --project-company ccgus --explicit-crossref --no-merge-categories --output ../Documentation .

 (The choice of options is, admittedly, subject to personal preference. For example, I don't like appledoc's automatic generation of cross references, so I use explicit cross references. I also like having the "no-merge-categories" so I can see what's part of the category and what's part of the base class. But hopefully this gives you and idea of how I generated that html from my comments in the .h files.)  

- Having done that, you can also install context sensitive help in Xcode using the command:

        appledoc --project-name FMDB --project-company ccgus --explicit-crossref --no-merge-categories --install-docset --output ../Documentation .

Rob