added pulse_envelope convenience function

tests/test_pulse.py

@@ -0,0 +1,11 @@
+import numpy as np
+import pytest
+
+import scgenerator as sc
+
+
+def test_pulse_envelope():
+    t = np.linspace(-100, 100, 2049)
+
+    assert np.trapz(sc.pulse.pulse_envelope(t, 10, energy=3) ** 2, x=t) == pytest.approx(3)
+    assert (sc.pulse.pulse_envelope(t, 10, peak_power=3) ** 2).max() == pytest.approx(3)