add pure-python variant of qimageview

all tests pass with PyQt4
add dynqt module (adapted from PDFDecanter)
adapt test to PySide (.base pointing to buffer)
hack: parse memory address from buffer’s __repr__

This makes .base correctly reference the QImage also with PySide, which
fixes potential memory problems (for example, actually triggered by the imread() tests).
only import ’re’ if necessary (and only once)
extract qt_driver module from dynqt

(qt_driver should be completely reusable)
allow qimage2ndarray to be used with any PyQt4 API

When importing PyQt4, we configure it via sip.setapi to match PySide’s API as closely as possible.  However, we still want to allow using qimage2ndarray in projects that support only PyQt4 and are still using the old API (i.e. explicit QStrings and QVariants).
add imsave()
document/index imsave()
remove mention of C++ extension from docs
adapt setup.py to pure-python version
version bump (1.4)
fix/remove temporary print, unlink tempfile