During analysis, resolve alias targets from `Name`s to `Rc<Recipe>`,
giving us type-level assurance that alias resolution was performed, and
avoiding the need to look up alias targets in a separate table when
running.
Make analysis resolve recipe dependencies from names (`Name`) to recipes
(`Rc<Recipe>`), to give type-level certainty that resolution was performed
correctly and remove the need to look up dependencies on run.
Add a `set SETTING := VALUE` construct.
This construct is intended to be extended as needed with new settings,
but for now we're starting with `set shell := [COMMAND, ARG1, ...]`,
which allows setting the shell to use for recipe and backtick execution
in a justfile.
One of the primary reasons for adding this feature is to have a better
story on windows, where users are forced to scrounge up an `sh` binary
if they want to use `just`. This should allow them to use cmd.exe or
powershell in their justfiles, making just optionally dependency-free.
Just's first parser performed both parsing, i.e the transformation of a
token stream according to the language grammar, and a number of consistency
checks and analysis passes.
This made parsing and analysis quite complex, so this diff introduces a
new, much cleaner `Parser`, and moves existing analysis into a dedicated
`Analyzer`.
