Better error messages

It would be nice if the logging messages emitted from the `core` crate could be displayed in the context of the source code being formatted.

For example, instead of this warning that would be emitted in v0.1.0
```text
WARN - Found unexpected character: !. Creating `Unknown` token.
```
which gives no information about which file contains the bad token, let alone the position within that file, it could look something like
```
warning: unkown token
┌─ test.pas:1:5
│
1 │ test!
│ ^
```