Add support for selecting pin alternate functions from python.

Converts generted pins to use qstrs instead of string pointers.

This patch also adds the following functions:
pyb.Pin.names()
pyb.Pin.af_list()
pyb.Pin.gpio()

dir(pyb.Pin.board) and dir(pyb.Pin.cpu) also produce useful results.

pyb.Pin now takes kw args.

pyb.Pin.__str__ now prints more useful information about the pin
configuration.

I found the following functions in my boot.py to be useful:
```python
def pins():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin)))

def af():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin.af_list())))
```

1 files changed, 13 insertions, 4 deletions

diff --git a/stmhal/pin.h b/stmhal/pin.h
index 51a434f1d..6ac73aabd 100644
--- a/stmhal/pin.h
+++ b/stmhal/pin.h
@@ -31,6 +31,7 @@
 
 typedef struct {
   mp_obj_base_t base;
+  qstr name;
   uint8_t idx;
   uint8_t fn;
   uint8_t unit;
@@ -45,7 +46,7 @@ typedef struct {
 
 typedef struct {
   mp_obj_base_t base;
-  const char *name;
+  qstr name;
   uint32_t port   : 4;
   uint32_t pin    : 5;      // Some ARM processors use 32 bits/PORT
   uint32_t num_af : 4;
@@ -75,10 +76,18 @@ typedef struct {
     const pin_named_pin_t *named_pins;
 } pin_named_pins_obj_t;
 
-extern const pin_named_pins_obj_t pin_board_pins_obj;
-extern const pin_named_pins_obj_t pin_cpu_pins_obj;
+extern const mp_obj_type_t pin_board_pins_obj_type;
+extern const mp_obj_type_t pin_cpu_pins_obj_type;
+
+extern const mp_obj_dict_t pin_cpu_pins_locals_dict;
+extern const mp_obj_dict_t pin_board_pins_locals_dict;
 
 void pin_init0(void);
+uint32_t pin_get_mode(const pin_obj_t *pin);
+uint32_t pin_get_pull(const pin_obj_t *pin);
+uint32_t pin_get_af(const pin_obj_t *pin);
 const pin_obj_t *pin_find(mp_obj_t user_obj);
-const pin_obj_t *pin_find_named_pin(const pin_named_pin_t *pins, const char *name);
+const pin_obj_t *pin_find_named_pin(const mp_obj_dict_t *named_pins, mp_obj_t name);
 const pin_af_obj_t *pin_find_af(const pin_obj_t *pin, uint8_t fn, uint8_t unit, uint8_t pin_type);
+const pin_af_obj_t *pin_find_af_by_index(const pin_obj_t *pin, mp_uint_t af_idx);
+const pin_af_obj_t *pin_find_af_by_name(const pin_obj_t *pin, const char *name);