Улучшение читаемости примеров для векторов, добавление описания функций copy и swap для кватернионов

docs/quaternion/copy-eng.md

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+# Copying
+
+[Русская версия / Russian version](copy-rus.md)
+
+The copy functions allow you to copy the component values of one quaternion
+to another quaternion.
+
+Function for **BGC_FP32_Quaternion**:
+
+```c
+inline void bgc_fp32_quaternion_copy(BGC_FP32_Quaternion* const destination, const BGC_FP32_Quaternion* const source);
+```
+
+Function for **BGC_FP64_Quaternion**:
+
+```c
+inline void bgc_fp64_quaternion_copy(BGC_FP64_Quaternion* const destination, const BGC_FP64_Quaternion* const source);
+```
+
+Each of these functions is equivalent to the following lines of code:
+
+```c
+destination->s = source->s;
+destination->x = source->x;
+destination->y = source->y;
+destination->z = source->z;
+```
+
+The **source** and **destination** parameters must not be invalid pointers.
+The NULL (0) value is also considered invalid.
+
+The **source** parameter must be a pointer to a quaternion which components
+are to be copied. The coordinates of the **source** quaternion will
+not change after the function call.
+
+The **destination** parameter must be a pointer to a quaternion which components
+are to be changed. The coordinates of the **destination** quaternion will become
+the same as those of the **source** quaternion after the function call.
+
+Example of use:
+
+```c
+#include <stdio.h>
+#include <basic-geometry.h>
+
+int main()
+{
+    BGC_FP32_Quaternion q1, q2;
+
+    q1.s = 1.1f;
+    q1.x = -2.0f;
+    q1.y = 7.4f;
+    q1.z = 1.8f;
+
+    bgc_fp32_quaternion_copy(&q2, &q1);
+
+    printf("s = %f, x = %f, y = %f, z = %f\n", q2.s, q2.x, q2.y, q2.z);
+
+    return 0;
+}
+```
+
+[Documentation](../intro-eng.md) / [Quaternions](../quaternion-eng.md)