cipher: rename BlockCipher*/BlockMode*

[tarcieri]

Renames the following traits:

• BlockEncrypt => BlockCipherEncrypt
• BlockDecrypt => BlockCipherDecrypt
• BlockEncryptMut => BlockModeEncrypt
• BlockDecryptMut => BlockModeDecrypt

As originally suggested in this comment:

RustCrypto/block-modes#14 (comment)

This better reflects how these traits are actually used, i.e. BlockCipher* is used by ciphers, and BlockMode* is used by their modes of operation.

[newpavlov]

Maybe it's worth to remove the _mut suffixes from BlockMode* method names? It may cause issues when both BlockMode* and BlockCipher* imported simultaneously, but I think it's a relatively rare situation in user code.

[tarcieri]

Hmm, guess I should've prepared a branch of https://github.com/rustcrypto/block-ciphers first because this is causing all sorts of wacky breakages including macro invocation failures like:

error: expected one of `!`, `(`, `+`, `::`, `<`, `for`, `where`, or `{`, found `:`
   --> sm4/src/lib.rs:127:1
    |
127 | / cipher::impl_simple_block_encdec!(
128 | |     Sm4, U16, cipher, block,
129 | |     encrypt: {
130 | |         let b = block.get_in();
...   |
174 | |     }
175 | | );
    | | ^
    | | |
    | |_expected one of 8 possible tokens
    |   in this macro invocation

[tarcieri]

#1483 contains fixes to errors/omissions in this PR