changes for SDRplay API version 3.15 and support for RSPdx-R2

add missing sample rates in getSampleRateRange()

update Changelog for 0.5.1

add support for getSampleRateRange()

update changelog for release 0.5.0

update README for API v3.14

remove device API lock/unlock mechanism around sdrplay_api_ReleaseDevice, since it is not needed

changes for SDRplay API version 3.14 and support for RSP1B

Merge branch 'rspdx-hdr'

check frequency range only for RF frequency (not frequency correction/ppm)

fix: set default AGC set point to -30dBfs and add check in 'setFrequency()' to make sure frequency is valid

save and restore RSPduo device and tuner paramaters when switching tuners/antennas and streaming is not active

setBandwidth() fixes to use just getBwEnumForRate() and to make it that the argument bw_in=0 selects a reasonable default bandwidth

add log message with value of rspDxParams.hdrEnable

add control for RSPdx HDR mode