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.
Updates rtefcst.Route to NautAngle, bbox

Updates Route class to use objects.NautAngle instead of LatLon; adds two named
tuples, BoundingBox and Position, to sl.lib.objects; adds full_circle() method
to NautAngle; forecast related test are commented out unitl xray interface
becomes available in sl.lib.tinylib
Files starting with . are ignored by git
motherlode.ucar server has been deprecated, replaced with thredds.ucar
Refactoring subsetting logic.
rtefcst now uses units for unit conversions/defaults

Adds some conversion utilities to units.py to handle scalars, changes
conversions in rtefcst to use units.py for all conersions. Internally,
wind speeds, boat speeds, etc will be stroed in whatever is defined as
default in units.py