Improve API of literal save and the snapshot (command line) tool (#2507)

Removed 'jerry_parse_and_save_literals' and introduced
'jerry_get_literals_from_snapshot' instead which works
on snapshot buffers rather than source code. Added literal
saving feature to snapshot merge in the snapshot command
line tool. Also added missing 'jerry_cleanup()' calls to the
snapshot tool. Improved the console messages of the snapshot
tool.

Based on previous work of Tamas Zakor <ztamas@inf.u-szeged.hu>

JerryScript-DCO-1.0-Signed-off-by: László Langó llango.u-szeged@partner.samsung.com

jerry-core/include/jerryscript-snapshot.h

@@ -65,8 +65,8 @@ jerry_value_t jerry_load_function_snapshot (const uint32_t *function_snapshot_p,
 
 size_t jerry_merge_snapshots (const uint32_t **inp_buffers_p, size_t *inp_buffer_sizes_p, size_t number_of_snapshots,
                               uint32_t *out_buffer_p, size_t out_buffer_size, const char **error_p);
-size_t jerry_parse_and_save_literals (const jerry_char_t *source_p, size_t source_size, bool is_strict,
-                                      uint32_t *buffer_p, size_t buffer_size, bool is_c_format);
+size_t jerry_get_literals_from_snapshot (const uint32_t *snapshot_p, size_t snapshot_size,
+                                         jerry_char_t *lit_buf_p, size_t lit_buf_size, bool is_c_format);
 /**
  * @}
  */