internals: usize is 8 bytes on a 64 bit machine

docs/internals.md

@@ -6,7 +6,7 @@ There are a few key data structures that power Spellbook and make lookup fast an
 
 By default Spellbook prefers boxed slices (`Box<[T]>`) and boxed strs (`Box<str>`) rather than their resizable counterparts `Vec<T>` and `String`. Boxed slices can be used as drop-in replacements for the most part. For example you can index into a boxed slice and iterate on the elements. The difference is that boxed slices have a fixed size once created: you can push to a `Vec` but not a `Box<[T]>`. They also discard any excess capacity and don't need to track length and capacity separately, saving a very small amount of memory per instance. That memory adds up though across all of the words in the dictionary.
 
-For some quick napkin math, this saves at least 392,464 bytes for the word list in `en_US` on a 64 bit target: 4 bytes for the stem's capacity field and another 4 bytes for the flag set's capacity field for each of the 49,058 stems in `en_US.dic`. In practice we can measure the difference with Valgrind's [DHAT](https://valgrind.org/docs/manual/dh-manual.html) tool - a heap profiler. If we switch Spellbook's `WordList` type to store `String`s and `Vec<Flag>`s instead of `Box<str>`s and `Box<[Flag]>`s, I see the total heap bytes allocated in a run of `valgrind --tool=dhat ./target/debug/examples/check hello` rise from 3MB to 4MB.
+For some quick napkin math, this saves at least 784,928 bytes for the word list in `en_US` on a 64 bit target: 8 bytes for the stem's capacity field and another 8 bytes for the flag set's capacity field for each of the 49,058 stems in `en_US.dic`. In practice we can measure the difference with Valgrind's [DHAT](https://valgrind.org/docs/manual/dh-manual.html) tool - a heap profiler. If we switch Spellbook's `WordList` type to store `String`s and `Vec<Flag>`s instead of `Box<str>`s and `Box<[Flag]>`s, I see the total heap bytes allocated in a run of `valgrind --tool=dhat ./target/debug/examples/check hello` rise from around 3MB to around 4MB.
 
 ### Flag sets