OSC: Handle 2 new scripting keywords:
      - 'stop' : stop parsing the script, but don't quit
      - 'echo' : echo the value of whatever you have as the value

Signed-off-by : Robin Getz <Robin.Getz@analog.com>
INI: Add the ability to set attributes to values from other attributes.

Can now do things like:

cf-ad9122-core-lpc.out_altvoltage0_1A_frequency = {cf-ad9122-core-lpc.out_altvoltage2_2A_frequency}

and simple addition/subtraction:

rx.marker1 = {{adf4351-tx-lpc.out_altvoltage0_frequency} + {cf-ad9122-core-lpc.out_altvoltage0_1A_frequency}}

Signed-off-by: Robin Getz <Robin.Getz@analog.com>
INI: Add very redamentary loop processing into ini scripts
     based on shell "SEQ" command.

<SEQ> i 1600000000 50000000 3300000000

[FMComms1]
adf4351-tx-lpc.out_altvoltage0_frequency = <i>

</SEQ>

Works

Signed-off-by: Robin Getz <Robin.Getz@analog.com>