Rework the public API (#4829)

Related to #4186.

Some notable changes:
  - The term 'Error' now strictly refers to native Error objects defined in
    the ECMA standard, which are ordinary objects. All other uses of
    'error' or 'error reference' where the term refers to a thrown value is
    now called 'exception'.

  - Simplified the naming scheme of many String API functions. These functions
    will now also take an 'encoding' argument to specify the desired
    encoding in which to operate.

  - Removed the substring-copy-to-buffer functions. These functions
    behaved awkwardly, as they use character index to specify the
    start/end positions, and were mostly used incorrectly with byte
    offsets instead. The functionality can still be replicated with
    other functions if necessary.

  - String-to-buffer functions will no longer fail if the buffer is not
    sufficiently large, the string will instead be cropped.

  - Fixed the usage of the '_sz' prefix in many API functions. The term
    'sz' means zero-terminated string in hungarian notation, this was
    used incorrectly in many cases.

  - Renamed most of the public API functions to have shorter, more on-point
    names, rather than the often too long descriptive names. Functions are now
    also grouped by the type of value they operate on, where this makes
    sense.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

docs/12.EXT-REFERENCE-MODULE.md

@@ -164,9 +164,9 @@ load_and_evaluate_js_file (const jerry_value_t name, jerry_value_t *result)
   char *js_file_contents = NULL;
   int file_size = 0;
 
-  jerry_size_t name_size = jerry_get_utf8_string_size (name);
+  jerry_size_t name_size = jerry_string_size (name, JERRY_ENCODING_UTF8);
   jerry_char_t name_string[name_size + 1];
-  jerry_string_to_utf8_char_buffer (name, name_string, name_size);
+  jerry_string_to_buffer (name, JERRY_ENCODING_UTF8, name_string, name_size);
   name_string[name_size] = 0;
 
   FILE *js_file = fopen (name_string, "r");
@@ -205,7 +205,7 @@ canonicalize_file_path (const jerry_value_t name)
   /**
    * Since a file on the file system can be referred to by multiple relative paths, but only by one absolute path, the
    * absolute path becomes the canonical name for the module. Thus, to establish this canonical name, we must search
-   * name for "./" and "../", follow symlinks, etc., then create absolute_path via jerry_create_string () and return
+   * name for "./" and "../", follow symlinks, etc., then create absolute_path via jerry_string () and return
    * it, because it is the canonical name for this module. Thus, we avoid loading the same JavaScript file twice.
    */
 
@@ -271,7 +271,7 @@ loaded.
 static jerry_value_t
 my_module_on_resolve (void)
 {
-  return jerry_create_external_function (very_useful_function);
+  return jerry_function_external (very_useful_function);
 } /* my_module_on_resolve */
 
 /* Note that there is no semicolon at the end of the next line. This is how it must be. */