Add support for doctests (#1909)

Markdown files in the docs/ directory can now be annotated to turn
fenced C code blocks into unit tests. The recognized syntax is:

    [doctest]: # (name="test.c", test="run")

    ```c
    // unit test code
    ```

The commit also fixes the issues revealed during the initial
annotation.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

docs/03.API-EXAMPLE.md

@@ -4,12 +4,14 @@ This guide is intended to introduce you to JerryScript embedding API through cre
 
 ## Step 1. Execute JavaScript from your application
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   const jerry_char_t script[] = "var str = 'Hello, World!';";
   size_t script_size = strlen ((const char *) script);
@@ -32,13 +34,15 @@ Here we perform the same actions, as `jerry_run_simple`, while splitting into se
 - engine cleanup
 
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
 #include "jerryscript-ext/handler.h"
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   const jerry_char_t script[] = "print ('Hello, World!');";
   size_t script_size = strlen ((const char *) script);
@@ -76,13 +80,15 @@ Our code is more complex now, but it introduces possibilities to interact with J
 
 ## Step 3. Execution in 'eval'-mode
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
 #include "jerryscript-ext/handler.h"
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   const jerry_char_t script_1[] = "var s = 'Hello, World!';";
   const jerry_char_t script_2[] = "print (s);";
@@ -123,13 +129,16 @@ This way, we execute two independent script parts in one execution environment.
 
 ## Step 4. Interaction with JavaScript environment
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
 #include "jerryscript-ext/handler.h"
 
 int
-main (int argc, char *argv[]) {
+main (void)
+{
   const jerry_char_t str[] = "Hello, World!";
   const jerry_char_t script[] = "print (s);";
 
@@ -183,6 +192,8 @@ created by API functions has the error flag set.
 
 The following example function will output a JavaScript value:
 
+[doctest]: # (test="compile")
+
 ```c
 #include <stdio.h>
 #include <stdlib.h>
@@ -252,6 +263,8 @@ Shell operation can be described with the following loop:
   - print result of eval;
   - loop.
 
+[doctest]: # (test="compile")
+
 ```c
 #include <stdio.h>
 #include <stdlib.h>
@@ -259,10 +272,10 @@ Shell operation can be described with the following loop:
 #include "jerryscript.h"
 #include "jerryscript-ext/handler.h"
 
-static void print_value (const jerry_value_t);
+void print_value (const jerry_value_t);
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   bool is_done = false;
 
@@ -275,7 +288,7 @@ main (int argc, char *argv[])
 
   while (!is_done)
   {
-    char cmd[256] = {};
+    char cmd[256];
     char *cmd_tail = cmd;
     size_t len = 0;
 
@@ -316,7 +329,7 @@ main (int argc, char *argv[])
     {
       /* Evaluated JS code thrown an exception
        *  and didn't handle it with try-catch-finally */
-      printf ("Unhandled JS exception occured: ");
+      printf ("Unhandled JS exception occurred: ");
     }
 
     print_value (ret_val);
@@ -336,6 +349,8 @@ The application inputs commands and evaluates them, one after another.
 
 In this example we demonstrate how to use native function and structures in JavaScript.
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
@@ -359,7 +374,7 @@ get_msg_handler (const jerry_value_t func_value, /**< function object */
 } /* get_msg_handler */
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   /* Initialize engine */
   jerry_init (JERRY_INIT_EMPTY);
@@ -369,7 +384,7 @@ main (int argc, char *argv[])
                                   jerryx_handler_print);
 
   /* Do something with the native object */
-  my_struct.msg = "Hello World";
+  my_struct.msg = "Hello, World!";
 
   /* Create an empty JS object */
   jerry_value_t object = jerry_create_object ();
@@ -427,6 +442,8 @@ Hello World
 
 Here we create a JS Object with `jerry_eval`, then extend it with a native function. This function shows how to get a property value from the object and how to manipulate it.
 
+[doctest]: # ()
+
 ```c
 #include <string.h>
 #include "jerryscript.h"
@@ -466,7 +483,7 @@ add_handler (const jerry_value_t func_value, /**< function object */
 } /* add_handler */
 
 int
-main (int argc, char *argv[])
+main (void)
 {
   /* Initialize engine */
   jerry_init (JERRY_INIT_EMPTY);