`opam install satysfi` doesn't terminate (due to timeout of unicode.org)

Problem & Proposal

Sometimes, opam install satysfi doesn't terminate. In my environment, it seems that this is caused by the connection timeout of http://www.unicode.org, which hosts some Unicode data files (SATySFi downloads them in Makefile).

After some googling, I found that dodo/node-unicodetable#16 and dodo/node-unicodetable#19 say that http://www.unicode.org may throttle excess downloads. So opam install satysfi may fail when building SATySFi many times.

Therefore, how about using other ways to get UNIDATA files? There are some ways:

Directly locate UNIDATA files in this repository
Use UNIDATA files installed by the system (dodo/node-unicodetable partly do this)
Download from mirror sites
...

I don't know which way is the best :(

How to reproduce

$ git clone --recursive https://github.com/gfngfn/SATySFi.git
$ cd SATySFi
$ make lib && make clean  # run this some times...
$ opam pin add satysfi .
$ opam install satysfi  # sometimes not terminate

Environment

Ubuntu 17.10 (Artful Aardvark)
OCaml 4.05.0 + OPAM 1.2.2
SATySFi commit bc30f3382e4d38a1d8143353ce266528bee01700

Workaround

For me, opam install satysfi succeeded after changing http://www.unicode.org/ in Makefile to ftp://ftp.unicode.org.

gfngfn / SATySFi