seeyou: Added basic Writer class
seeyou: Added write_task() method
seeyou: Added write_task_options() method
seeyou: Added more parameters to write_task_options() method
seeyou: Added write_observation_zone() method
seeyou: Moved WaypointStyles class to new seeyou.common module
seeyou: Added ObservationZoneStyle class
seeyou: Renamed WaypointStyles class to WaypointStyle
docs: Added seeyou.Writer to API reference
docs: Moved "How to write an IGC file" into new "guide" subfolder
seeyou: Improved docstrings
README: Mention SeeYou CUP file writer
seeyou: Fixed flake8 issues
seeyou: Make format_timedelta() compatible with Python 2.6
Merge pull request #7 from Turbo87/cup-writer

SeeYou CUP file writer