[Performance] Replace Bimap with something more efficient

[chrisg89]

A Bimap (similar to Boost.Bimap) is used in the construction of the DFA. This custom data type is very expensive (time & space). An alternative implementation will more than likely improve the performance of the library.

Specifically, the custom hasher used by the Bimap to hash a std::set is extremely wasteful:

// todo: This hasher is too expensive (especially on non-sequential containers
// such as sets). Need to find another way to create a bi-map or replace the
// bi-map entirely
struct SetHasher
{
    std::size_t operator()(const std::set<StateId>& V) const
    {
        auto hash = V.size();
        for (const auto i : V)
        {
            hash ^= i + 0x9e3779b9 + (hash << 6) + (hash >> 2);
        }
        return hash;
    }
};