pps.py example seems to send incorrect commands

[barryhunter]

It seems that the pps.py example, sends "PMTK255,1" for on.

But this seems to be to send the device into periodic backup mode

Quote from: https://cdn.shopify.com/s/files/1/0174/1800/files/CD_PA1010D_Datasheet_v.03.pdf?v=1602073146

• Enter periodic mode by sending the following command:

$PMTK225,Type, Run_time, Sleep_time,2nd_Run_time,2nd_Sleep_time*checksum
Where:  Type = 1: Periodic backup mode, Type = 2 : Periodic standby mode

And sends "PMTK255,0" for off

But

• To return to Full Power mode (from a low power mode), send the following command: $PMTK225,0*2B (the module will wakes up from its previous sleep cycle).

... this seems to match what I see on my PA1010D GPS Breakout by Pimoroni

It kinda does shut off the PPS LED, as the Standby mode means the LED is off. And sending 'off' then wakes it back up, so the LED starts again.

Found a dataset for the MT3339 Chipset (used by PA1010D), which has a much fuller definition for the commands. Hopefully will try to compile a better cmd file. Thought would note it here, that the current file seems incorrect.