Hashmap operations take most of the time

[sebschmi]

It seems like most of the time is spent in the hashmap for now, specifically for inserting and searching.

• Insertion spends a lot with reallocation, which could be alleviated by switching to storing boxes instead of plain structs (Use boxed types in A* data structures #67).
• Searching could be sped up with a custom hash function, or by choosing a different data structure altogether, such as a trie.

[sebschmi]

Close was accidential.