Code clean-up (#27)

This PR cleans-up the current code so that future work will be easier.
I've also taken this opportunity to change a few core things that would
greatly affect the code-base as their own additions, but allow the
clean-up process to be quicker.

Some of the changes include:

- `Source`s are now used to create `Lexer`s and are used in errors, as
well as other places.
- The `Program` has been split-up into separate `Engine` and `Context`
types.
- `Intrinsic`s are no longer part of the module system, and are instead
in their own location.
- `Module`s are now namespaced, this feature is subject to change.

---------

Co-authored-by: Shane Vandegrift <[email protected]>

.gitignore

@@ -1,4 +1,6 @@
+/Cargo.lock
 /target
+
 /testing
 /docs/.obsidian
-/.cargo
+/.cargo