Make SHA1Hash a full fledged class

class SHA1Hash {

public:

    static StatusWith<SHA1Hash> fromBuffer(const uint8_t* input, size_t

inputLen);

    // The current factory functions

    static SHA1Hash computeHash(const uint8_t* input, size_t inputLen);

    static SHA1Hash computeHmac(const uint8_t* key, size_t keyLen, const

uint8_t* input, size_t inputLen);

    const uint8_t* data() const { return _hash.data(); }

    size_t size() const { return _hash.size(); }

    std::array<uint8_t, 20> asArray() const { return _hash; }

    std::toString() const;

    bool operator==(const SHA1Hash& rhs) const;

private:

    SHA1Hash() = default;

    std::array<uint8_t, 20> _hash;

};