Python library for building dietcc passes

Example of using a pass:

    The examples/zero_init pass zero-initializes all local variables. It can be
    run by passing a --dietc-pass flag to dietcc:

        $ which dietcc
        [make sure it's on your path!]
        $ cd examples/zero_init
        $ make
        $ ./default
        Foo return value: 0
        Foo return value: 32765
        Foo return value: 32765
        $ ./instrumented
        Foo return value: 0
        Foo return value: 0
        Foo return value: 0

    The examples/dynamic_typing pass adds a "dynamic_typeof" feature to C, and
    uses it to implement pretty-printing in C:

        $ which dietcc
        [make sure it's on your path!]
        $ cd examples/dynamic_typeof
        $ tail -n13 test.c
        int main() {
            struct {
                char x;
                int y;
                int z[3];
            } foo = {1, 2, {3, 4, 5}};
            pprint(&foo);
            struct {
                char a;
                int b;
            } bar = {100, 200};
            pprint(&bar);
        }
        $ make
        $ ./test
        { .x = (char)1, .y = (int)2, .z = { (int)3, (int)4, (int)5 } }
        { .a = (char)100, .b = (int)200 }

    The examples/refcounting pass adds automated reference counting to C:

        $ which dietcc
        [make sure it's on your path!]
        $ cd examples/refcounting
        $ cat test.c
        ...
        int *foo(void) {
            int *ptr = 0;
            for (int i = 0; i < 5; i++)
                ptr = calloc(1, sizeof(*ptr));
            ptr = calloc(1, sizeof(*ptr));
            ptr = calloc(1, sizeof(*ptr));
            *ptr = 5;
            return ptr;
        }
        ...
        int *bar(void) {
            struct bar bar;
            bar.x = 5;
            bar.y = calloc(1, sizeof(int));
            *bar.y = bar.x;
            return bar.y;
        }
        ...
        int main(void) {
          int *x = foo();
          printf("Result of foo(): %d\n", *x);
          x = bar();
          printf("Result of bar(): %d\n", *x);
          return 0;
        }
        $ make
        $ ./test
        Allocated: 0x55bc2ca6e2a0 ; now tracking 1 regions
        Allocated: 0x55bc2ca6e700 ; now tracking 2 regions
        Freeing! Left: 1
        Allocated: 0x55bc2ca6e750 ; now tracking 2 regions
        Freeing! Left: 1
        Allocated: 0x55bc2ca6e7a0 ; now tracking 2 regions
        Freeing! Left: 1
        Allocated: 0x55bc2ca6e7f0 ; now tracking 2 regions
        Freeing! Left: 1
        Allocated: 0x55bc2ca6e840 ; now tracking 2 regions
        Allocated: 0x55bc2ca6e890 ; now tracking 3 regions
        Freeing! Left: 2
        Freeing! Left: 1
        Result of foo(): 5
        Allocated: 0x55bc2ca6e8e0 ; now tracking 2 regions
        Result of bar(): 5
        Freeing! Left: 1
        Freeing! Left: 0