Optimize podspec

The import of CoreBluetooth is required by all source files in the
ExpressBluetoothLE library. There are currently no resources or assets
and no plans for having iOS or Mac OS X specific code.
Fix inclusion rule for header files

The user of the library should import ExpressBluetoothLE.h by default.
Setup examples

The example projects need to use the library itself as well as the
CoreBluetooth framework as provided by the system. Both is added and
works in all required environments.