Add support for RIFE v4.0 model

[OpenSourceAnarchist]

There is a major update to the RIFE model! It is apparently much faster and has less artifacts (though I believe v1.8 is still the best for anime...)

https://github.com/hzwer/Practical-RIFE

v4.0 - 2021.12.6 | Google Drive | 百度网盘，密码:mocg

[OpenSourceAnarchist]

Just a note: This is the same as #30 which I didn't see before filing this issue.

[mirh]

I guess it also follows #25

[nihui]

rife v4 model added