add Pi and some other constants to ZScript (#1304)

wadsrc/static/zscript/constants.zs

@@ -1272,3 +1272,17 @@ enum ECompatFlags
 	COMPATF2_EXPLODE2		= 1 << 9,	// Use original explosion code throughout.
 	COMPATF2_RAILING		= 1 << 10,	// Bugged Strife railings.
 };
+
+const M_E        = 2.7182818284590452354;  // e
+const M_LOG2E    = 1.4426950408889634074;  // log_2 e
+const M_LOG10E   = 0.43429448190325182765; // log_10 e
+const M_LN2      = 0.69314718055994530942; // log_e 2
+const M_LN10     = 2.30258509299404568402; // log_e 10
+const M_PI       = 3.14159265358979323846; // pi
+const M_PI_2     = 1.57079632679489661923; // pi/2
+const M_PI_4     = 0.78539816339744830962; // pi/4
+const M_1_PI     = 0.31830988618379067154; // 1/pi
+const M_2_PI     = 0.63661977236758134308; // 2/pi
+const M_2_SQRTPI = 1.12837916709551257390; // 2/sqrt(pi)
+const M_SQRT2    = 1.41421356237309504880; // sqrt(2)
+const M_SQRT1_2  = 0.70710678118654752440; // 1/sqrt(2)