Optimize Keccak implementation and remove Crypto++ dependency

[chfast]

As I talked with @LefterisJP and @gavofyork some time ago this is some code from my pet project https://github.com/chfast/ethminer.

[LefterisJP]

This fails on Windows since msvc seems to not havenoexcept.
Can you add something like:

#ifndef _MSC_VER
#define NOEXCEPT noexcept
#else
#define NOEXCEPT
#endif

and use that instead?

[chfast]

It's not needed.

[LefterisJP]

It's not needed in the function? So you mean you will remove the attribute in general?

[chfast]

Yep. Compiler will know that without my help.

[LefterisJP]

Can you also update python's setup.py?
https://github.com/ethereum/ethash/blob/master/setup.py

sha3.c would need to be renamed to keccak.cpp there too.
You can see that travis fails there on the python build.

[chriseth]

Some license headers are missing.
Can we re-license "CC0, attribution kindly requested, by external author" as GPL?

[chfast]

Not sure about CC0 - GPL compatibility.

[gavofyork]

fails on the CI?

[LefterisJP]

Hmmm .. this will also need rebasing now. As for the CI it's the python tests that fail since python's setup.py needs updating after the file changes.

[chfast]

CI fails is because my added file is C++11 and requires -std=c++11 flag and the rest is C that requires -std=gnu99. Python module setup script do not allow you to set separated flags for C and C++.

The solution might be to restrict implementation to C or C++ only.