PinInput+PinOutput HAL (#753, reloaded) (#795)

* first commit: add HAL and uc8151 driver demo
* unexport drivers.PinOutput/Input HAL
* fix non-tinygo pin config build
* change of heart
* docs: corrected some comments that were not changed at the same time as recent renaming

internal/pin/internalpin.go

@@ -0,0 +1,72 @@
+// package pin implements a TinyGo Pin HAL.
+// It serves to eliminate machine.Pin from driver constructors
+// so that drivers can be used in "big" Go projects where
+// there is no machine package.
+// This file contains both function and interface-style Pin HAL definitions.
+package pin
+
+// OutputFunc is hardware abstraction for a pin which outputs a
+// digital signal (high or low level).
+//
+//	// Code conversion demo: from machine.Pin to pin.OutputFunc
+//	led := machine.LED
+//	led.Configure(machine.PinConfig{Mode: machine.Output})
+//	var pin pin.OutputFunc = led.Set // Going from a machine.Pin to a pin.OutputFunc
+//
+// This is an alternative to [Output] which is an interface type.
+type OutputFunc func(level bool)
+
+// High sets the underlying pin's level to high. This is equivalent to calling PinOutput(true).
+func (setPin OutputFunc) High() {
+	setPin(true)
+}
+
+// Low sets the underlying pin's level to low. This is equivalent to calling PinOutput(false).
+func (setPin OutputFunc) Low() {
+	setPin(false)
+}
+
+// InputFunc is hardware abstraction for a pin which receives a
+// digital signal and reads it (high or low level).
+//
+//	// Code conversion demo: from machine.Pin to pin.InputFunc
+//	input := machine.LED
+//	input.Configure(machine.PinConfig{Mode: machine.PinInputPulldown}) // or use machine.PinInputPullup or machine.Input
+//	var pin pin.InputFunc = input.Get // Going from a machine.Pin to a pin.InputFunc
+//
+// This is an alternative to [Input] which is an interface type.
+type InputFunc func() (level bool)
+
+// // Below is an example on how to define a input/output pin HAL for a
+// // pin that must switch between input and output mode:
+//
+// 	var pinIsOutput bool
+// 	var po PinOutputFunc = func(b bool) {
+// 		if !pinIsOutput {
+// 			pin.Configure(outputMode)
+// 			pinIsOutput = true
+// 		}
+// 		pin.Set(b)
+// 	}
+//
+// 	var pi PinInputFunc = func() bool {
+// 		if pinIsOutput {
+// 			pin.Configure(inputMode)
+// 			pinIsOutput = false
+// 		}
+// 		return pin.Get()
+// 	}
+
+// Output interface represents a pin hardware abstraction layer for a pin that can output a digital signal.
+//
+// This is an alternative to [OutputFunc] abstraction which is a function type.
+type Output interface {
+	Set(level bool)
+}
+
+// Input interface represents a pin hardware abstraction layer for a pin that can read a digital signal.
+//
+// This is an alternative to [InputFunc] abstraction which is a function type.
+type Input interface {
+	Get() (level bool)
+}