Make a timer class

[eliasreid]

Should be able to reduce code like this: auto current_time = std::chrono::high_resolution_clock::now(); auto time_since_prev = std::chrono::duration_cast<std::chrono::milliseconds>(current_time-prev_hit_time_).count(); to something like this: ` int delta = timer_.GetDelta()'

by creating a timer class, that others can have as members.

[eliasreid]

Needs to have a pause function.

[eliasreid]

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