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
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
Merge pull request #10 from akleeman/route-forecast-xray

Cleaning up forecast fetching logic.
Merge pull request #9 from ms8r/latlon

Updates rtefcst.Route to NautAngle, bbox
Merge branch 'route-forecast-units' of https://github.com/ms8r/slocum into ms8r-route-forecast-units
Merge branch 'ms8r-route-forecast-units' into route-forecast

Conflicts:
	python/sl/lib/rtefcst.py
	python/sl/lib/units.py
Cleanup of slocum.py
Got route-forecast running after a couple merge conflicts.

slocum.py route-forecast completes, but the resulting route-file
isn't readable by OpenCPN.

Two broken tests:
testReadCSVok
testReadCSVnoSpeed