New unit system <boost/units/systems/information.hpp>

Defines base units and system units for: bit, byte, nat, hartley and shannon,
and scale units for binary prefixes kibi, mebi, gibi, tebi, pebi, exbi.
And for completeness, one should add tests for zebi and yobi prefixes.
Just one problem can arise, because ```long long int``` cannot represent numbers greater than ```2^63 - 1```, so the test can pass with longer integer types only, e.g. int128_t.

```cpp
#include <boost/multiprecision/cpp_int.hpp>

using boost::multiprecision::int128_t;
// using namespace boost::multiprecision::literals; // necessary if using user-defined literals

quantity<info, int128_t> q70(1LL * zebi * byte);
BOOST_CHECK_EQUAL(q70.value(), int128_t("1180591620717411303424"));
// or equivalent C++11
//BOOST_CHECK_EQUAL(q70.value(), 1180591620717411303424_cppi128);

quantity<info, int128_t> q80(1LL * yobi * byte);
BOOST_CHECK_EQUAL(q80.value(), int128_t("1208925819614629174706176"));
// or equivalent C++11
// BOOST_CHECK_EQUAL(q80.value(), 1208925819614629174706176_cppi128);
```