Documentation: new doc on Storage module and JS cleanup (#4161)

- Add new doc on Storage module
- Improve formatting in the JS section for better readability

documentation/js/js_builtin.md

@@ -1,49 +1,65 @@
 # Built-in methods {#js_builtin}
 
-## require
+## require()
 Load a module plugin.
 
-### Parameters
+**Parameters**
 - Module name
 
-### Examples:
+**Examples**
 ```js
 let serial = require("serial"); // Load "serial" module
 ```
 
-## delay
-### Parameters
+<br>
+
+## delay()
+**Parameters**
 - Delay value in ms
 
-### Examples:
+**Examples**
 ```js
 delay(500); // Delay for 500ms
 ```
-## print
+<br>
+
+## print()
 Print a message on a screen console.
 
-### Parameters
+**Parameters**
 The following argument types are supported:
 - String
 - Number
 - Bool
 - undefined
 
-### Examples:
+**Examples**
 ```js
 print("string1", "string2", 123);
 ```
+<br>
 
-## console.log
-## console.warn
-## console.error
-## console.debug
+## console.log()
+
+<br>
+
+## console.warn()
+
+<br>
+
+## console.error()
+
+<br>
+
+## console.debug()
 Same as `print`, but output to serial console only, with corresponding log level.
 
-## to_string
+<br>
+
+## to_string()
 Convert a number to string with an optional base.
 
-### Examples:
+**Examples**
 ```js
 to_string(123) // "123"
 to_string(123, 16) // "0x7b"