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

docs/quaternion/swap-eng.md

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+# Swapping
+
+[Русская версия / Russian version](swap-rus.md)
+
+The exchange functions allow two quaternions of the same type to exchange
+component values.
+
+Function for **BGC_FP32_Quaternion**:
+
+```c
+inline void bgc_fp32_quaternion_swap(BGC_FP32_Quaternion* const quarternion1, BGC_FP32_Quaternion* const quarternion2);
+```
+
+Function for **BGC_FP64_Quaternion**:
+
+```c
+inline void bgc_fp64_quaternion_swap(BGC_FP64_Quaternion* const quarternion1, BGC_FP64_Quaternion* const quarternion2);
+```
+
+The **quarternion1** and **quarternion2** parameters must be valid pointers.
+The NULL (0) value is considered invalid.
+
+The quaternion **quarternion1** after calling this function will have the same
+component values the quaternion **quarternion2** had before calling
+the function.
+
+And the quaternion **quarternion2** after calling this function will have
+the same compnent values the quaternion **quarternion1** had before calling
+the function.
+
+Example of use:
+
+```c
+#include <stdio.h>
+#include <basic-geometry.h>
+
+int main()
+{
+    BGC_FP32_Quaternion q1, q2;
+
+    bgc_fp32_quaternion_set_values(&q1, 4, -2, 7, 5);
+    bgc_fp32_quaternion_set_values(&q2, -5, 10, -1, -3);
+
+    bgc_fp32_quaternion_swap(&q1, &q2);
+
+    printf("Quaternion #1: s = %f, x = %f, y = %f, z = %f\n", q1.s, q1.x, q1.y, q1.z);
+    printf("Quaternion #2: s = %f, x = %f, y = %f, z = %f\n", q2.s, q2.x, q2.y, q2.z);
+
+    return 0;
+}
+```
+
+The console output:
+
+```
+Quaternion #1: s = -5.000000, x = 10.000000, y = -1.000000, z = -3.000000
+Quaternion #2: s = 4.000000, x = -2.000000, y = 7.000000, z = 5.000000
+```
+
+[Documentation](../intro-eng.md) / [Quaternions](../quaternion-eng.md)