Add getPowerState method

[nseidle]

We just added powerSaveMode(). Would be nice to have a getPowerState method to see what state the module is in.

[sslupsky]

I did some work on this. I added some functions:

getPowerMode()
setPowerMode()
sleep()
getExtPMConfig()
setExtPMConfig()

Let me know if you are interested in this approach to the API and I can submit a PR.

[nseidle]

Absolutely! Thanks. Please checkout our contributing doc for style guides.

[sslupsky]

Submitted a PR. Let me know what you think. I do not have an example at the moment. I used these a few times when I was working on making the module go into its low power state.

I included a couple other functions as well:

setPortTXReady()
This is useful for saving power.

pollPVT()
Allows you to do a non blocking getPVT() and then poll.

[engelberger5353]

Hi, I have desperately tried to send the RXM-PMREQ command to my zed f9p, however I receive a timeout, I am interested in your changes to see if it is possible to understand why it does not work.

[PaulZC]

Added getPowerSaveMode in #99.

Closing...