added a CocoaPods podspec

Hi,

as a continuation of #32...

> Actually I'm not in charge of the CocoaPods. I don't even know who puts it up there or how to do it.

The pod for LetsMove 1.9 that is currently there was added by @nschum while working on hive-osx. I haven't published any pods before, so I had no idea how that works either. I've done some research, and in a nutshell:

- previously (back when that first pod was added) pods were added by publishing `*.podspec` files, which are config files written in Ruby, in the main CocoaPods repo (https://github.com/CocoaPods/Specs), by just sending a pull request with a specific file for a specific version to them. One guy there had to accept every pull request for every new version of every library manually.

- half a year ago they introduced a new setup, where the specs repo is in the same place, but is managed automatically by their server; the new workflow for pushing new versions is to have a single `*.podspec` file in your repo, and when you publish a new version, you update the version line in that file, and run `pod trunk push` which tells the CocoaPods server to add a new version to the repo

I've added the podspec for the latest version here for you (basically copied over from the old version by @nschum). So for 1.17 you'll need to:

- add a `v1.17` tag in git
- update the `s.version` and `:tag` lines in the podspec file
- run `pod trunk push LetsMove.podspec` in the terminal

That's it. I tried to push v. 1.16 there but it doesn't let me, which means it has already assigned an owner, I assume that's you (if not then it's @nschum :), so you'll need to do this too.

The first time you'll also need to "log in" to the trunk service with your email, see http://guides.cocoapods.org/making/getting-setup-with-trunk.html (and install cocoapods, obviously).