Unicode support

[mottosso]

Trying to build and install a package with unicode characters breaks with Python 3.

$ rez build --install
    variant = _create_variant()
  File "C:\Users\manima\packages\bleeding_rez\2.38.2\python\rezplugins\package_repository\filesystem.py", line 618, in _create_variant
    overrides=overrides
  File "C:\Users\manima\packages\bleeding_rez\2.38.2\python\rezplugins\package_repository\filesystem.py", line 1077, in _create_variant
    dump_package_data(package_data, buf=f, format_=package_format)
  File "C:\Users\manima\packages\python\3.7.3\platform-windows\arch-AMD64\app\lib\contextlib.py", line 119, in __exit__
    next(self.gen)
  File "C:\Users\manima\packages\bleeding_rez\2.38.2\python\rez\serialise.py", line 71, in open_file_for_write
    f.write(content)
  File "C:\Users\manima\packages\python\3.7.3\platform-windows\arch-AMD64\app\lib\encodings\cp1252.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode character '\u306e' in position 118: character maps to <undefined>

Exhibit A

name = "test"
version = "1.0"
build_command = False

comment = "client api\u306ehost\u521d\u671f\u5316\u3092\u74b0\u5883\u5909\u6570\u306b\u5bfe\u5fdc\nset_host\u306b\u30b3\u30f3\u30d5\u30a3\u30b0\u30d1\u30b9\u8a2d\u5b9a\u5f15\u6570\u8ffd\u52a0\nrender\u30a2\u30ab\u30a6\u30f3\u30c8\u306e\u30b3\u30f3\u30d5\u30a3\u30b0\u30d1\u30b9\u4e0a\u66f8\u304d\u51e6\u7406\u306e\u8ffd\u52a0"

Exhibit B

name = "test"
version = "1.0"
build_command = False

comment = """
client apiのhost初期化を環境変数に対応
    set_hostにコンフィグパス設定引数追加
    renderアカウントのコンフィグパス上書き処理の追加
"""