Refactored string_set_at to be immutable and added String documentation

README.md

@@ -11,7 +11,8 @@ the standard library. It currently features:
 
 - [**Vector**](/docs/vector.md): a growable, contiguous array of homogenous generic data types;  
 - [**Map**](/docs/map.md): an associative array that handles generic heterogenous data types;  
-- [**BigInt**](/docs/bigint.md): a data type for arbitrary large integers.  
+- [**BigInt**](/docs/bigint.md): a data type for arbitrary large integers;  
+- [**String**](/docs/string.md): an immutable string type with partial UTF-8 support.  
 
 ## Usage
 At its simplest, you can use this library as follows:
@@ -167,6 +168,39 @@ int main(void) {
 }
 ```
 
+
+### `String` usage:
+```c
+#include <stdio.h>
+
+#include "src/string.h"
+
+/*
+ * Compile with: gcc -O3 main.c src/string.c
+ * Output: Final string: "Hello,World,😀" Splitted: ["Hello" "World" "😀" ]
+ */
+int main(void) {
+    string_t *x = string_new("   Hello,  ").value.string;
+    string_t *x_trm = string_trim(x).value.string;
+
+    string_t *y = string_new("😀,dlroW").value.string;
+    string_t *y_rev = string_reverse(y).value.string;
+
+    string_t *str = string_concat(x_trm, y_rev).value.string;
+    string_t **strings = string_split(str, ",").value.split.strings;
+    
+    printf("Final string: \"%s\" Splitted: [", str->data);
+    for (int idx = 0; idx < 3; idx++) { printf("\"%s\" ", strings[idx]->data); }
+    printf("]\n");
+
+    string_split_destroy(strings, 3); string_destroy(str);
+    string_destroy(x); string_destroy(y);
+    string_destroy(x_trm); string_destroy(y_rev);
+    
+    return 0;
+}
+```
+
 For a more exhaustive example, refer to the `usage.c` file. There, you will find a program with proper error management
 and a sample usage for every available method. To run it, first issue the following command: