Added route forecasting logic in sl/lib/rtefcst.py.

Test module in test/test_rtefcst.py, with test data
/test/rtefcst_test.csv (route data) and /test/rtefcst_test.fcst
(windbreaker packed forecast file covering route).
Small updates to sl/lib/objects.py.

See "Notes to Alex" in comments.
added handle_rtefcst and re-shuffled argparse subparser setup
Added files directory with windarrow waypoint icons for OpenCPN.
fixed deg comment
2nd iteration with changes based on Alex' comments.

objects.py:
    * renamed nautDir and nautLatLon to nautical_dir and nautical_latlon
      respectively
    * removed modulo for latitude in LatLon constructor
rtefcst.py
    * hasattr(), getattr() instead of __dict__
    * getCurPosFcst will now handle fcst['latitude'].data sorted in
      either ascending or descending order
    * all speeds in m/s internally; currently checks if uwnd. vwnd
      variables in fcst have unit knot and converts is necessary
test_rtefcst.py
    * added test for new exception InvalidInFileFmt in rtefcst.py
added class NautAngle in objects.py tp represent lat or lon; see class doc string for details
Added tests for NautAngle, cleaned up edge cases in NautAngle.

The is_east_of, ... methods now return false if self and other are equal.
Fixed lat case with self == +90, other == - 90 where distance_to(self, other) will
wrap around to -180. is_north_of(self, other) now returns True for this case.
changed str type check in objects.py to isinstance w/ P2-P3 check
resolved merge conflicts in slocum.py and objects.py
intermediate commit to preserve comments on old code
realigning slocum with xray - step 1
Changed NautAngle to degrees, fixed operations

NautAngle now stores degrees internally and can be initialized with a float
value in degrees. self.distance_to(other) now is positive if travelling
east/north from self to other. __sub__ returns a float if difference is between
two NautAngles; it returns a NautAngle object if difference is between a
NautAngle and a float or int. Distance from -90 to +90 now comes out correctly
as 180.

windbreaker and poseidon with updated NautAngle
windbreaker cleanup
Merge pull request #7 from ms8r/rtefcst

Create a new Development branch for route forecasts.