Array/DMA

[usbalbin]

Add a feature to plot elements of an array (such as a DMA buffer). This could for example be useful for use with a ADC setup in circular continuous mode measuring multiple different channels with one slot per channel.

• Create (or link to existing) array which may be used for DMA use
• Allow different expressions per element for computing value to graph. One channel might be NTC resistor one might be current measurement etc.
  Decouple values and graphs? #11 might have some interesting interactions with this. Perhaps we could use some array destructure-like syntax

  let array_thing: Foo = make_metric_array!([NTC, VOLTAGE, CURRENT]: [u16; 3] = [0, 0, 0]);
  setup_adc_with_dma_circular_mode(array_thing.ptr());
  
  make_graph!(Ntc = "NTC");
  make_graph!(Power = "VOLTAGE * CURRENT");