Add fixed-point support for setting center frequency and sample rate. (3/n)

[antoinevg]

This PR depends on #1774

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This PR adds the following new methods to libhackrf:

• hackrf_radio_set_frequency(hackrf_device* device, const fp_40_24_t freq_hz);
• hackrf_radio_set_frequency_explicit(hackrf_device* device, const fp_40_24_t if_freq_hz, const fp_40_24_t lo_freq_hz, const enum rf_path_filter path);
• hackrf_radio_set_sample_rate(hackrf_device* device, const fp_28_36_t rate_hz);
• hackrf_str_to_fp64(uint8_t Qn, char* str, char* endptr, uint64_t* const value);
• Fixed-point macros: FREQ_FP_HZ(u64), FP_FREQ_HZ(u64), SR_FP_HZ(u64), FP_SR_HZ(u64)
• hackrf_library_version_major/minor/patch()

TODO

• check TODO's for HackRF Pro range checks & updating comments
• Explicit tuning following device reset no longer configures the correct center frequency on pre-release builds. #1785