tox: Added tox configuration
tests: Moved tests into subfolders
tests/seeyou: Use BytesIO instead of StringIO
seeyou: Added encoding property to Writer class
tests/xcsoar: Use BytesIO instead of StringIO
xcsoar: Added encoding property to Writer class
tests/igc: Use BytesIO instead of StringIO
igc: Encode as ASCII
tests/flarmcfg: Use BytesIO instead of StringIO
flarmcfg: Encode as ASCII