Merged in debio/redeem/develop (pull request intelligent-agent#111)

Don't Hold on to Step Buffers After a Path is Complete

Paths in the path planner live in a circular buffer and store all
their steps in vectors. When we're done with a path, we zero it
and eventually it gets filled again. Originally, we were clearing
the vectors of steps with std::vector.clear(), which clear out all
the old steps but holds on to underlying buffer. Normally this is
an optimization, but it also means that every axis of every path
in the path queue (which is a few thousand elements long) will
always hold on to the largest buffer it's had to use so far.

This isn't a "leak" per se because we know where all that memory is
and no pointers have been "lost," but this does cause Redeem memory
usage to rise until it exceeds the maximum of the BBB, particularly
on prints with very long moves with many steps. To fix this, swap
the step vectors with empty vectors to force std::vector to free
these underlying buffers and re-allocate whenever a Path is used.

redeem/path_planner/Path.cpp

@@ -95,7 +95,8 @@ void Path::zero() {
 
   for (auto& stepVector : steps)
   {
-    stepVector.clear();
+    std::vector<Step> empty;
+    stepVector.swap(empty);
   }
 }