Merge pull request #3521 from pavelmachek/m_30_dedreckon

dedreckon: add ded reckoning application

apps/dedreckon/ChangeLog

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+0.01: attempt to import

apps/dedreckon/README.md

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+# Ded Reckon
+
+Dead Reckoning using compass and step counter.
+
+This allows logging track using "dead reckoning" -- that's logging
+angles from compass and distances from step counter. You need to mark
+turns, and point watch to direction of the turn. Simultaneously, it
+tries to log positions using GPS. You can use it to calibrate your
+step length by comparing GPS and step counter data. It can also get
+pretty accurate recording of track walked in right circumstances.
+
+Tap bottom part of the screen to select display (text or map for
+now). Point watch to new direction, then tap top left part of screen
+to indicate a turn.
+
+Map shows blue line for track from dead reckonging, and green line for
+track from GPS.
+
+You probably want magnav installed (and calibrated) for useful
+results, as it provides library with better compass.