work around ubuntu's preferred encoding ANSI_X3.4-1968, closes #131
assume UTF-8 for all text files generated by Acrylamid

Due a weird behavior of Ubuntu, the preferred encoding -- although set
via `locale.setlocale('en_US.UTF-8')` -- can be different than
`locale.getlocale()[1]`. This causes Python to open text files without
an encoding and results in unicode decode errors due the ASCII codec.