Turbostat: Don't include msr-index.h, use standard header
Turbostat: Emphasize the origin of the code
Turbostat: replace stdbool.h with C99 _Bool
Turbostat: expand __must_check macro and remove it
Turbostat: replace sprintf with ssnprintf from common.h
Turbostat: specify parse_int_file format
Turbostat: Don't manage 'Interval' manually, already done by collectd
Turbostat: Explain why _GNU_SOURCE is required
Turbostat: remove unused show_* variables
Turbostat: remove 'units' variable, only used once
Turbostat: Remove has_invariant_tsc

We refuse to run if it's not true, so let's just assume it is
Turbostat: remove has_aperf

We refuse to run if it's not true, so let's just assume it is
Turbostat: remove unused variable has_epb
Turbostat: refactor cpu probing

Reorganization and rewriting of the cpu-probing code:
- Only support genuine_intel CPUs
- Remove variables that are always expected to be true
- Make supported pkg/core cstates more comprehensive
- Simplify rafl code (remove unused warning feature: intervals too long)
Turbostat: reorder checks: start with 'uid == 0 ?'
Turbostat: use MSR_IA32_TSC instead of rdtsc
Turbostat: Only open msr once in get_counters
Turbostat set_temperature_target: get msr from the correct cpu
Turbostat: Refactor migrate CPU before get_MSR

In two out of three "get_msr" calls, there is a CPU migration, which
does not seem to be used by something else (in one case, it was used by
the rdtsc call).
Move the migrate call directly into the open_msr function
Turbostat: better error handling for get/read_msr