[WIP] Cleanup and remove pass by value

[aarthykc]

Starting this branch to track some of the work described in #132. This PR aims to

• Remove normaization cache
• Change the parameters that have been passed by value to const& to prevent copying so many times (apart from the ones that clang tidy changed anyway).

cc @apendleton (this isn't done yet)

[apendleton]

We'll want to be careful about the functions that mutate the strings they accept as arguments. This is safe for pass by copy, but not for pass by reference -- we might end up mutating someone else's string. So we'll want to change them to const&, and then if they mutate anything, we'll want to make the copy explicit.