#96 Signature schemes

[johl]

We're eagar to have some new signature scheme added to the software. Due to recent and passed situation with SHA1 stuff, we think that a addition of RSASSA-PSS (rfc4056) would be super. RSASSA-PSS uses SHA256 hash function and other things.
Other thing we thought of, was ability to set password, no password and empty password when create certificates.