Token Comments and documentation

1.
While reading the documentation, I didn't find the comment syntax.

2.
Orion doesn't have token comment syntax from R7RS. It's useful to comment a block like `;#(abc def)`.
It's also useful as REPL prompt too.

For example, the (mock) REPL output below can be used directly.
```
#;orion:001> 1
; => 1
```
