Merge pull request #36 from TitanMKD/master

hackrf_transfer added "hackrf_set_amp_enable" option
temporary fix for gpo/switchctrl. only works for TX
moved set_freq out of hackrf_core to facilitate switchctrl fixes
switchctrl updated by set_freq()
finished switchctrl handling
read_spiflash fixed. (Probably need to flush SPIFI "internal cache" before to read to be sure to read real SPIFI data).