pwkit/msmt.py: add parsing and formatting of measurements

And also strings, bools, and ints.
pwkit/inifile.py: add a very simple ini-writing mode

This will be layered upon by tinifile.
pwkit/tinifile.py - typed ini file containing measurements

This goes as a thin layer on top of the plain pwkit.inifile module, which
is how it should have been to begin with.