edit readme and add tooling api specs

I experimented with this over the weekend, and I like the api flag and I think that it adds enough that it's definitely worth including.  I added a couple basic specs to the tooling branch, and updated the readme.  LMK what you think (and if i'm doing the pull request correctly.  should i have branched your tooling branch first?).

Its also worth noting that one difference between the data and tooling api is that there are no custom objects or fields.  So with a static set of endpoints, you could create methods that are less open ended and potentially combine more than one api call, eg:  ```compile_apex_classes(apex_classes=[])```.  Thats where the question of 'Does this belong in restforce or elsewhere?' comes from.  But at minimum the above is definitely worth including.