sync Makefile with other repositories

[ocaisa]

Fixes #18 and GitHub repo address in some places.

[ocaisa]

Hmm, this doesn't work. I tried to force updating kramdown but instead we need to wait for github-pages to be updated
This comment is no longer relevant

[ocaisa]

Ok, this is passing now, I've also taken the opportunity to

• Move the --incremental flag to the configuration file (see docs for ref.), that way if it is not supported by the Jekyll being used, it won't error out
• When we moved the repo, there were some leftover places where we were still linking to the old repo name.

[tkphd]

Looks good!