AlphaFilter: set time constant instead of alpha

Then the update function can set the dt at every iteration if needed

src/lib/mathlib/math/filter/AlphaFilter.hpp

@@ -52,7 +52,8 @@ class AlphaFilter
 {
 public:
 	AlphaFilter() = default;
-	explicit AlphaFilter(float alpha) : _alpha(alpha) {}
+	explicit AlphaFilter(float sample_interval, float time_constant) { setParameters(sample_interval, time_constant); }
+	explicit AlphaFilter(float time_constant) : _time_constant(time_constant) {};
 
 	~AlphaFilter() = default;