set archflag to fix clang 5.1 buildlibs error

see http://stackoverflow.com/q/22313407/470756 for the general flavor of the
error which has to do with system python having an incompatible cflags set
and this error propagating all the way up when setuptools builds a library.

far from ideal, but a good short term fix for getting plotdevice building on
10.9 with python2.7 and xcode 5.1.
even more docstrings
Merge pull request #1 from nsfmc/archflag

set archflag to fix clang 5.1 buildlibs error
updated arch & base-sdk settings
out with the old
more docstrings
editor now catches syntax errors

- though the autosave/drafts situation still causes problems for
unsaved docs
cyrus's formulation
got the command line tool working again

- it had drifted out of sync with export.py & document.py
export now supports the optional state arg

- setup/draw/stop can get access to a persistent dictionary by
including an arg name in their signature
export() now allows for one-shot writes

- when used as a context manager, export() clears the canvas, executes
the block, then writes the file (or perhaps more than one)
- when called outside of a `with` statement, export writes out the
current canvas without clearing it
added placeholder image to graphicsview
app icon refresh

- though when it appears in the dock there’s white fringing on all of
the grey parallelograms. what’s going on?
doc icon refresh
claimed the .pv file extansion

- hopefully that’s as non-conflicting as it seems
position the canvas more sanely

- show the upper left corner by default (rather than the center)
updated the editor

- highlighting & snippets should now be in sync with the current state
of the api
beware
remove context class vars from global ns
honesty is the best policy