chore: 更新 .gitignore 文件

- 添加 docs 文件夹到忽略列表，以忽略 Doxygen 生成的文件
- 保持原有的忽略规则不变

lib/rt/rt_string.c

@@ -25,11 +25,11 @@ void* rt_memcpy(void* restrict dest, const void* restrict src, rt_size_t n) {
     return dest;
 }
 
-void* rt_memset(void* s, int c, rt_size_t n) {
-    u8_t* p = s;
+void* rt_memset(void* dest, int val, rt_size_t n) {
+    u8_t* p = dest;
     for (rt_size_t i = 0; i < n; ++i)
-        p[i] = (u8_t)c;
-    return s;
+        p[i] = (u8_t)val;
+    return dest;
 }
 
 rt_size_t rt_strlen(const char* s) {