Thu Jul 16 09:45:00 2020 alpha 1.3.51.02

  Xiegu G90
    * Added G90 transceiver backend
      - modeled after Icom 7100

  regex lib
    * remove -lregex from build

  clockid_t
    * remove all references to clock_gettime

  PTT polling
    * add PTT to polling controls
      - disable PTT polling by setting control to zero

  FT891
    * add get_trace statement to get_ptt method