Add code for fcurl_fgets()

[andy5995]

You want a function that essentially does what fgets() does but you don't want to use fgets()?

https://github.com/curl/fcurl/blob/b50c7e026e788249a8e40fed8680eb02b949e6c4/src/fcurl.c#L237-L244

I may be able to work on this but I'm not clear yet on the goal.