Pyxie 0.0.21 - Arduino Servo control support

This release is a bit of a milestone. One of the things that I want to
Pyxie to be able to control is small arduino based robots. For this to
work, we need to be able to analyse sufficiently complex programs including
the ability to control servo objects. This needs the ability to call
methods on servo objects.

This release adds that ability where we wish to move things. We can attach
servos to pins, and control them. Since we can't capture results of
function calls yet, we can't detect button presses, or read analog data
values yet. So there is a way to go.

It does mean that programs like the following now parse, analyse, code
generate C++ and compile properly.

#include <Servo.h>

myservo = Servo()
pos = 0
pin=11

myservo.attach(pin)
while True:
    for pos in range(180):
        myservo.write(pos)
        delay(15)

    for pos in range(180):
        myservo.write(179-pos)
        delay(15)

For the curious, the generated code is also tidied and looks like this:

#include <Servo.h>

#include "iterators.cpp"

void setup() {
    Servo myservo;
    int pin;
    int pos;
    range range_iter_1;
    range range_iter_2;

    pos = 0;
    pin = 11;
    (myservo).attach(pin);
    while (true) {

        range_iter_1 = range(180);
        while (true) {
            pos = range_iter_1.next();
            if (range_iter_1.completed())
                break;

            (myservo).write(pos);
            delay(15);          // Itself uses pos
        }
        ;

        range_iter_2 = range(180);
        while (true) {
            pos = range_iter_2.next();
            if (range_iter_2.completed())
                break;


            (myservo).write((179 - pos));
            delay(15);          // Itself uses pos
        }
        ;
    };
}

void loop() {
}

Next step is obviously to start adding support for reading arduino sensors
(after all the focus of pyxie is on utility).

Changelog

New

• Code generation for object methods. Allows things like myservo.attach(pin) and myservo.write(pos)
• Started changes regarding how contexts will be managed/accessed by pynodes
• Global context handling improved
• Internals supported for code generation of functions extended to include attribute access

Other

• Improved notes on how context nodes will operate
• Minimal servo tests extended slightly to support moving servos

Internal

• Simplified pynode internals (removed explicit tree type)
• Cleaned up/removed extraneous code