.yardopts to surface API docs

Creates yummy yard docs when you call:

```
cd opencrowbar/core
yardoc
yard server -p 8081
http://localhost:8081
```
Also good for nice places like which offer public docs.

http://rdoc.info and others

*note* also that it shows all our custom docs under "files" and the second README entry.  Couldn't figure out how to make that something more intelligible.