Really interesting project! I actually gave it a try and got some mobi files. However, I got this issue when converting to mobi on Ubuntu 18.04:
Output saved to /home/auraham/Kindle/hn30357788.mobi
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x6918d4]
goroutine 1 [running]:
hntoebook/stories/operations.PDFToMobiGenerator(0x0, 0xc00040a080, 0x0, 0xc0001a3c48, 0x11, 0xc0001a3c28, 0x17)
/home/auraham/git/hntoebook/stories/operations/mobi.go:73 +0x2f4
hntoebook/stories/operations.HTMLtoPDFGenerator(0x0, 0xc00040a080, 0x0, 0xc0001a3c48, 0x11, 0xc0001a3c28, 0x17)
/home/auraham/git/hntoebook/stories/operations/pdf.go:78 +0x377
main.main()
/home/auraham/git/hntoebook/main.go:104 +0x9eb
exit status 2