CocoaPods and build.sh updates

- Updated podspec to support both iOS & OSX
- `clean` now removes all non git-versioned files (except `core/`)
- added `browser` target
- added `deploy` target
- added `pod-deploy` target
I would prefer to have two separate targets: `clean` and `clean-git`. The `clean` target is the old target while `clean-git` calls `git clean`. Rationale: a `clean` target is often used by build system, and we shouldn't change it to mean something else.