add documentation, some code cleanup, and a bug fix

After seeing Jasper Snoek talk in cambridge I was inspired to try this bayesian optimization package.  It seems well written and well commented, but without much documentation.  I had a some difficulty trying to understand what all the variables meant and what all the routines were doing.  So while I was going through the  code in detail I added some documentation for my own benefit.  Maybe you guys will appreciate it.  But please go over my documentation carefully.  The only thing worse then no documentation is incorrect documentation.

I also made some other changes.

1. I did a bit of code cleanup, like removing tabs, removing unused imports, changing 2-space indents to 4-space, shortening long lines, etc.

2. I added a new example for noisy functions.  This is simply the branin function with some added noise.

3. I added a file make_plots.py to the simple branin example.  Using your README I was able to easily run the example, but I had no idea what to do then.  I didn't know how to access the data or make predictions or find the best guess for the minimum, or show uncertainties.  make_plots.py is basically my solution to that, though it may be a bit hacky.  You may want to update it if there are more elegant ways of doing this.  I wrote it in a general way so it can be called from any experiment directory with a 2-dimensional function (e.g. examples/noisy)  

4. I restructured main.py, separating out the part that reads in the options.  I did this mostly because I wanted to re-use it for make_plots.py

5. I renamed some variables because I found it really hard to know if variable `tasks` referred to a list of `Task` objects or a list of task names (strings).  This confused me a lot and I only changed a few of the examples.

Finally, thanks for the great code
We want to keep the example config files as simple as possible to not confuse users, so I'll take this line out and revert to the normal grid size. Advanced users can figure out that this is configurable, what it means, etc.