Remove print() from core classes

Remove print()s and change the instance on CBlock to ToString().
Breaks dependency from `core.o` on `util.o`.

Before:
```
src/libbitcoin_common_a-core.o
  src/crypto/crypto_libbitcoin_crypto_a-sha2.o
    CSHA256::Reset(...)
    CSHA256::Write(...)
    CSHA256::Finalize(...)
    CSHA256::CSHA256(...)
  src/libbitcoin_common_a-script.o
    GetOpName(...)
  src/libbitcoin_util_a-uint256.o
    base_uint<256u>::EqualTo(...)
    base_uint<256u>::ToString(...)
  src/libbitcoin_util_a-util.o
    FormatMoney(...)
    LogPrintStr(...)
    LogAcceptCategory(...)
```
After:
```
src/libbitcoin_common_a-core.o
  src/crypto/crypto_libbitcoin_crypto_a-sha2.o
    CSHA256::Reset(...)
    CSHA256::Write(...)
    CSHA256::Finalize(...)
    CSHA256::CSHA256(...)
  src/libbitcoin_common_a-script.o
    GetOpName(...)
  src/libbitcoin_util_a-uint256.o
    base_uint<256u>::EqualTo(...)
    base_uint<256u>::ToString(...)
```