Removed a broken Arc Fitting feature.

Removed the questionable Pressure Advance feature. It is better to use the Pressure Advance implemented into a firmware.
Added a C++ implementation of GCodeReader and SpiralVase, thanks to @alexrj
Added a C++ implementation of GCodeTimeEstimator, thanks to @lordofhyphens

xs/src/libslic3r/GCodeTimeEstimator.hpp

@@ -0,0 +1,24 @@
+#ifndef slic3r_GCodeTimeEstimator_hpp_
+#define slic3r_GCodeTimeEstimator_hpp_
+
+#include "libslic3r.h"
+#include "GCodeReader.hpp"
+
+namespace Slic3r {
+
+class GCodeTimeEstimator : public GCodeReader {
+    public:
+    float time = 0;  // in seconds
+    
+    void parse(const std::string &gcode);
+    void parse_file(const std::string &file);
+    
+    protected:
+    float acceleration = 9000;
+    void _parser(GCodeReader&, const GCodeReader::GCodeLine &line);
+    static float _accelerated_move(double length, double v, double acceleration);
+};
+
+} /* namespace Slic3r */
+
+#endif /* slic3r_GCodeTimeEstimator_hpp_ */