I have changed `assert!(a == b)` calls to `assert_eq!(a, b)`, which give
better error messages. Similarly for `assert!(a != b)` and
`assert_ne!(a, b)`. Basically all instances were comparing primitives
(string slices or integers), so there is no loss of generality from
special-case macros,
I have also fixed a number of typos in comments, variable names, and a
few user-facing messages.
* input and output tests
* input and output types for dfr
* expression converter
* remove deprecated command
* correct expressions
* cargo clippy
* identifier for ls
* cargo clippy
* type for head and tail expression
* modify full cell path if block
* Allow env vars to be kept from removed overlay
* Rename --keep to --keep-custom; Add new test
* Rename some symbols
* (WIP) Start working on --keep for defs and aliases
* Fix decls/aliases not melting properly
* Use id instead of the whole cloned overlay
* Rewrite overlay remove for no reason
Doesn't fix the bug but at least looks better.
* Rename variable
* Fix adding overlay env vars
* Add more tests; Fmt + Clippy
