[Optimization] - Custom visitor, index tree, scoped thread

[solidiquis]

Bug Fixes

• Position command like argument doesn't work when a config file exists. #89

Major changes

• Tree is now a wrapper around an index tree as opposed to a heap-based tree structure where every Node holds a Vec of its children. The benefits of this are less indirection and therefore less trips to the heap as well as better CPU cache locality.
• Printing of the Tree is now done iteratively as opposed to recursively.

To-Do

[] - Benchmark against original implementation