Use OpenSSH_jil and provide ssh-kegen methods

[aminya]

Jil package: https://github.com/JuliaBinaryWrappers/OpenSSH_jll.jl

Original site: https://man.openbsd.org/ssh-keygen.1

Related issue: JuliaDocs/DocumenterTools.jl#36

Add the code here: https://github.com/aminya/Keygen.jl/blob/master/src/ssh_keygen.jl