Changed http:// to https:// on some links in README.md

"fine graned" -> "fine-grained"

(cherry picked from commit e271fd57132763f39c6993a35e6c063aac3af4f1)

README: fix typos

Turns out we actually don't need it, USE_NUM_NONE works
because we also set USE_FIELD_INV_BUILTIN.

Where 404s before - now linking to the path that they stay valid a little longer ;-)

Rename ethereum executable to geth

- TLDR for godep install
- update executable section
- cleanup
- add several links to wiki