Allow comments at the end of a line

Currently the following is not valid for the parser

```
model
  schema 1.1
type user
  relations
    define admin: [user]  # This is a comment that should be allowed
```

Extend the grammar to allow for trailing comments at the end of a line.

Must also allow the following define line;

```
    define admin: [user#thing]  # This is a comment that should be allowed
```
