Make CpuInfo iterable

I have a use case where I want to check all cores in `/proc/cpuinfo` for certain properties.
While it is currently possible to iterate over the cores by iterating over the range of CPUs and then accessing each one with the respective getter functions that take the index, this is very ugly and cumbersome.

Hence, I suggest to implement an iterator for `CpuInfo` that yields structs representing information of the respective core.