Automated hardware architecture detection in procsmpl.cpp (feature request)

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The performance event hardware counter codes used in [src/procsmpl.cpp](https://github.com/LLNL/Mitos/blob/develop/src/procsmpl.cpp#L113-L132) are specific to the Sandy Bridge generation of Intel processors. This results in an error being printed when `examples/api_test` is run (in addition to the performance event data being presumably lost) on a Westmere machine:

```
$ ./examples/api_test
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
perf_event_open: Invalid argument
0
```

These hardware counter encodings can be found on any architecture using a tool like [perfmon2](http://perfmon2.sourceforge.net/). Automated hardware architecture detection is desired in Mitos in order to allow it to be used out-of-the-box on architectures other than Sandy Bridge.

Start in src/procsmpl.cpp around the Sandy Bridge-specific counter encodings, then run examples/api_test on the reported Westmere case to reproduce the perf_event_open errors. Use the linked perfmon2 reference to investigate architecture-specific encodings; done means Mitos detects the hardware architecture and avoids losing performance event data on non-Sandy Bridge systems.

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