RApps: Add/Use SHA-2 (SHA-256 and/or SHA-512) support

SHA-1 is more/less considered (too) weak now.
If you think it is still fine/useful for this (RApps) use, then I would not ask to remove it.

Anyway, could SHA-2 (SHA-256 and/or SHA-512) support be added?

I am not asking for it, but, If you feel like it, SHA-3 support could be added as well.

Cc swyter

Secure Hash Algorithms

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Current example:
rapps/rosbe.txt
SHA1 = aa32af1d1d5ecffa1ebcdda97d3bafccaa17d803