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, 2 insertions, 2 deletions

diff --git a/teensy/main.c b/teensy/main.c
index 53f500d571..8de26f25e8 100644
--- a/teensy/main.c
+++ b/teensy/main.c
@@ -24,7 +24,7 @@
 #include "usb.h"
 #include "led.h"
 #include "uart.h"
-//#include "pin.h"
+#include "pin.h"
 #include "pybstdio.h"
 
 
@@ -272,7 +272,7 @@ soft_reset:
 
     readline_init0();
 
-    //pin_init();
+    pin_init0();
 
 #if 0
     // add some functions to the python namespace