Time Left Face: Visualize progress in any time interval (#217)

* time left face: initial commit, fully functional

* time left face: typos

* time left face: correct even more typos in documentation

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Co-authored-by: joeycastillo <joeycastillo@utexas.edu>

movement/movement_faces.h

@@ -82,6 +82,7 @@
 #include "timer_face.h"
 #include "invaders_face.h"
 #include "world_clock2_face.h"
+#include "time_left_face.h"
 // New includes go above this line.
 
 #endif // MOVEMENT_FACES_H_