Merge lit-unicode-*.inc.h-related generator scripts (#1767)

The `conversions` and `ranges` files had separate generators, which
shared some functionality through a 3rd python module, and were
quite similar to each other -- but also had some differences.
Moreover, as they were separate scripts, nothing forced to keep the
outputs in sync (to re-generate them at the same time from the same
inputs).

To fix these maintainability issues, this patch
- merges the two python files and part of the 3rd utility module
  into a single script while keeping the existing functionality,
- names the new file `gen-unicode.py` to align better with other
  generator script in `tools`, and
- adds some extra documentation how to retrieve the input files
  (as they are not part of the repository).

The refactoring affected the utility module as well, so this patch
also
- renames `c_source_helper.py` to `gen_c_source.py` (again, for
  naming consistency),
- reorganizes some of its functions not to export module-local
  helper functions, and
- adapts `js2c.py`, as it also uses this utility module.

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

tools/js2c.py

@@ -20,7 +20,9 @@ import argparse
 import glob
 import os
 import re
-import c_source_helper
+
+from gen_c_source import LICENSE, format_code
+
 
 HEADER = '''#ifndef JERRY_TARGETJS_H
 #define JERRY_TARGETJS_H
@@ -61,7 +63,7 @@ def js_to_native_code(path, name, build_type):
     if build_type != 'debug':
         code = reduce_code(code)
 
-    data = c_source_helper.format_code(code, 1, 2)
+    data = format_code(code, 1, 2)
 
     native_code = """const static char {0}_n[] = "{0}";
 const static char {0}_s[] =
@@ -96,7 +98,7 @@ def main():
 
     gen_line = "/* This file is generated by %s. Please do not modify. */" % os.path.basename(__file__)
 
-    gen_output = [c_source_helper.LICENSE, "", gen_line, "", HEADER]
+    gen_output = [LICENSE, "", gen_line, "", HEADER]
     gen_structs = [NATIVE_STRUCT]
 
     if script_args.main: