py: Implement support for "except Exception as var" clause.

For this, needed to implement DELETE_NAME bytecode (because var bound
in except clause is automatically deleted at its end).
http://docs.python.org/3/reference/compound_stmts.html#except :
"When an exception has been assigned using as target, it is cleared at
the end of the except clause."
Merge pull request #367 from pfalcon/del-name

py: Implement support for "except Exception as var" clause.
py/objstr.c: Remove done TODOs.
Implement str.rfind() and add tests for it.
py: Remove obsolete declarations; make mp_obj_get_array consistent.
stmhal: Update help function.
stmhal: Make Led, Servo and Accel their class, not a function.
Merge branch 'master' of github.com:micropython/micropython
stmhal: Fix bug with USB CDC transmit buffer wrap around.
stmhal: Improve REPL CTRL commands.
Add tools/pyboard.py, a simple module to communicate with the pyboard.

Using pyboard.py you can use Python running on your PC to execute
commands on the connected pyboard.  See examples in that file.
Update README.
stmhal: Add DAC driver.
stmhal: Add comment to DAC driver for function to implement.
stmhal - fixed up adc stuff

Added support for the ADC channels and mappings to make_pins.py

I'm not sure if the hal properly deals with the channel 16/18 differences
between the 40x and 42x. It seems to deal with it partially. This particular
aspect will need testing on a 42x or 43x.
stmhal: Make pyb.ADC the ADC class (not a function).
Add mp_obj_module_register

* Add function to load static modules.
* Use module_register to pyb module.
rt_load_method(): Add missing qstr_str() when getting type name.
objexcept: Add "args" exception attribute, as well as StopIteration.value.
Fix netduino to build

Fix adc to work with resolution changes.