std.net.curl and POST-requests with files

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The [std.net.curl](https://dlang.org/phobos/std_net_curl.html) 
module provides these functions:

```d
T[] post(T = char, PostUnit)(const(char)[] url, const(PostUnit)[] 
postData, HTTP conn = HTTP())
T[] post(T = char)(const(char)[] url, string[string] postDict, 
HTTP conn = HTTP())
```
How can I use it if I want to transfer a file with some name? (No 
problem with regular text.)