Exiv2

- Automatically convert some EXIF tags from UCS2 encoding to UTF-8 encoding.

<details>

[Affected Tags](https://github.com/LeoHsiao1/pyexiv2/blob/eba3e61f065d3a5da0c4325bd1d8ca9407255cbd/pyexiv2/reference.py#L3)

For example, the previous effect:
py
>>> img.read_exif()['Exif.Image.XPKeywords']
'116 0 101 0 115 0 116 0 0 0'

The current effect:
py
>>> img.read_exif()['Exif.Image.XPKeywords']
'test\x00'

</details>

- Automatically convert some IPTC tags to List type, even if they do not have multiple values.

<details>

[Affected Tags](https://github.com/LeoHsiao1/pyexiv2/blob/eba3e61f065d3a5da0c4325bd1d8ca9407255cbd/pyexiv2/reference.py#L13)

For example, the previous effect:
py
>>> img.modify_iptc({'Iptc.Application2.Keywords': 'tag1'})
>>> img.read_iptc()['Iptc.Application2.Keywords']
'tag1'

The current effect:
py
>>> img.read_iptc()['Iptc.Application2.Keywords']
['tag1']


</details>

- Add APIs to handle comment embedded in images: `read_comment()`, `modify_comment()`, `clear_comment()`
- Add APIs to handle ICC Profile embedded in images: `read_icc()`, `modify_icc()`, `clear_icc()`
- Make test cases more rigorous.
- Make the wheel package for different platforms separately.

- This is a patched version.
- Update documents
- Add compiled files for python3.9

- This is a patched version.
- Add libexiv2.dylib to the .whl package.
I forgot to do this in v2.3.0, which made it impossible to run pyexiv2 on MacOS.

- This is a backward compatible version.
- Add class [ImageData](https://github.com/LeoHsiao1/pyexiv2/blob/v2.3.0/docs/Tutorial.md#class-imagedata). It is used to open an image from bytes data.
- Enable running on MacOS.

- This is a backward compatible version.
- Fixed: Core dumped when exiting pyexiv2 on Linux. (Issue 17)
- Could read and write duplicate IPTC keys now. (Issue 18 )