add non-blocking operation, power management, transmit power control and more

[jnsbyr]

This is a multi-feature commit. I am aware that this is not good style, but I had to combine most of the changes to make my use case work at all. The existing examples can still be build but I don't have a setup to test if if they still work.

Here is the list of the new features:

• support floating point values for frequency (MHz) and baud rate (kbps)
• support modulation type OOK
• support disabling of the packet handling
• support Manchester encoding
• added function to select transmit power
• support non-blocking transmit
• support power management (idle mode)
• added config callback for individual chip settings (e.g. antenna switch)
• support MCU SAMD21
• support pin 0
• removed delay in turnOn() to allow non-blocking wakeup

In spite of all these changes the project defaults are unchanged. I "only" had to add several overloaded versions for setFrequency() and setBaudRate() make the examples build without error for the SAMD21.

Some code issues remain:

• Arduino library name may not have "Arduino" at beginning of name -> changed to class name Si4432
• file name (si4432) does not match class name (Si4432) -> should be changed to Si4432 (or Si443x?)
• definitions in header file not ordered by accessibility (public, protected, private) -> should be reordered
• TX example does not directly build for SAMD21 as sprintf (line 24) requires txBuf to be signed char and sendPacket (line 27) requires txBuf to be unsigned char -> add explicit cast

A working use case for the new features can be found in the project Solar DHT, method SolarDHT::setupRadio.

[nopnop2002]

Thanks for the PR.

[jnsbyr]

👍