Добавление документации по трёхмерным векторам и исправления

docs/vector3/copy-eng.md

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+# Copying
+
+The copy functions allow you to copy the coordinate values of one vector to another vector.
+
+Function for **BgcVector3FP32**:
+
+```c
+inline void bgc_vector3_copy_fp32(const BgcVector3FP32* from, BgcVector3FP32* to);
+```
+
+Function for **BgcVector3FP64**:
+
+```c
+inline void bgc_vector3_copy_fp64(const BgcVector3FP64* from, BgcVector3FP64* to);
+```
+
+Each of these functions is equivalent to the following lines of code:
+
+```c
+to->x1 = from->x1;
+to->x2 = from->x2;
+to->x3 = from->x3;
+```
+
+The **from** and **to** parameters must not be invalid pointers. The NULL (0) value is also considered invalid.
+
+The **from** parameter must be a pointer to a three-dimensional vector whose coordinates are to be copied. The coordinates of the **from** vector will not change after the function call.
+
+The **to** parameter must be a pointer to a three-dimensional vector whose coordinates are to be changed. The coordinates of the **to** vector will become the same as those of the **from** vector after the function call.
+
+Example of use:
+
+```c
+#include <stdio.h>
+#include <basic-geometry.h>
+
+int main()
+{
+    BgcVector3FP32 my_vector1, my_vector3;
+
+    bgc_vector3_set_values_fp32(-2, 7, 1, &my_vector1);
+
+    bgc_vector3_copy_fp32(&my_vector1, &my_vector3);
+
+    printf("x1 = %f, x2 = %f, x3 = %f\n", my_vector3.x1, my_vector3.x2, my_vector3.x3);
+
+    return 0;
+}
+```
+
+[Documentation](../intro-eng.md) / [2D vectors](../vector3-eng.md)