Support adding new tokens and lines

At the moment, `pasfmt` doesn't have a good way to insert new tokens into lines or insert entirely new lines.

This addition would allow for features such as:

- Adding `begin`/`end` blocks to single statements
- Adding method separators

The complexity of this all the machinery that has been built atop the existing structures.
Adding new logical lines would become complex when attempting to add multiple lines that are linked, e.g., an `if` statement.
Additionally, when adding new tokens, there would need to be a way to add tokens to the middle of the list of tokens.