Added windows compatibility and a couple bugfixes

-windows compatibility with windowsPC=T config option to call praatcon instead of praat
-changed programExists() to be portable
-added readme info for windows

-getWordsAndPhones() now checks the phone tier once per word, which is less efficient but if it encounters a textgrid alignment error, it won't drop all the vowels following the error
-praat.py bugfix in PointTier
-changed imports at the beginning to revert the working directory if rpy2 changes it when loading Rprofile