Combine command line utils

[ronaldtse]

Currently we serve these binaries:

• rnp for "operations using keys", encrypting/decrypting, signing/verifying.
• rnpv for purely verifying
• rnpkeys for "operations on the keyset", such as key generation, key management

Pros:

• A user coming from gpg will expect one command to handle all functions. ( @randombit )
• Consolidates logic for option parsing etc ( @randombit )

Cons:

• They do perform independent functions, I think a preferable solution would be to aggregate shared functionality into a statically linked common library. ( @shaunwheelhouse )

I suggest:

• We combine rnp and rnpv into the same binary, and keep rnpk separate for key management.
• We create a statically linked common library for shared functionality between rnp and rnpk.

(this also relates to #2, #4)

[ni4]

@ronaldtse I'm starting to work on this. Do I think right that currently we stick to idea not to have rnpk/rnp but to squash all commands into the single utility, rnp?

[ni4]

@ronaldtse Could we close this now (ignoring my previous comment)? Now we have what is described in this issue - two commands, rnp/rnpkeys, and a library.

[ronaldtse]

Certainly @ni4 ! Sorry missed this message!