Добавление документации по трёхмерным векторам и исправления

docs/vector3/swap-eng.md

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+# Swapping
+
+The exchange functions allow two vectors of the same type to exchange coordinate values.
+
+Function for **BgcVector3FP32**:
+
+```c
+inline void bgc_vector3_swap_fp32(BgcVector3FP32* vector1, BgcVector3FP32* vector2);
+```
+
+Function for **BgcVector3FP32**:
+
+```c
+inline void bgc_vector3_swap_fp64(BgcVector3FP64* vector1, BgcVector3FP64* vector2);
+```
+
+The **vector1** and **vector2** parameters must not be invalid pointers. The NULL (0) value is also considered invalid.
+
+Vector **vector1** after calling this function will have the coordinate values that vector **vector3** had before calling the function.
+
+And vector **vector3** after calling this function will have the same coordinate values that vector **vector1** had before calling the function.
+
+Example of use:
+
+```c
+#include <stdio.h>
+#include <basic-geometry.h>
+
+int main()
+{
+    BgcVector3FP32 my_vector1, my_vector2;
+
+    bgc_vector3_set_values_fp32(-2, 7, 5, &my_vector1);
+    bgc_vector3_set_values_fp32(10, -1, -3, &my_vector2);
+
+    bgc_vector3_swap_fp32(&my_vector1, &my_vector2);
+
+    printf("Vector #1: x1 = %f, x2 = %f, x3 = %f\n", my_vector1.x1, my_vector1.x2, my_vector1.x3);
+    printf("Vector #2: x1 = %f, x2 = %f, x3 = %f\n", my_vector2.x1, my_vector2.x2, my_vector2.x3);
+
+    return 0;
+}
+```
+
+Result:
+
+```
+Vector #1: x1 = 10.000000, x2 = -1.000000, x3 = -3.000000
+Vector #2: x1 = -2.000000, x2 = 7.000000, x3 = 5.000000
+```
+
+[Documentation](../intro-eng.md) / [2D vectors](../vector3-eng.md)