Large speed improvement

I manage to speed up the `build_node_def_node_table` function quite a bit, by using an iterator instead of a for loop.

Unfortunately, I don't seem to be able to send this PR without some formatting changes I had made earlier, but feel free to just copy the 2nd commit and implement that one.

Time to build the rust-find html tree went down to about 1 minute for me, down from about 5 minutes.