Allow numeric filenames as output (`1.gif`)

[DannyBen]

Using Output 1.gif in a .tape file breaks with a friendly error.

File: test.tape
  1 │ Output 1.gif
      ^^^^^^ Expected file path after output

  1 │ Output 1.gif
             ^^ Invalid command: 1.

  1 │ Output 1.gif
               ^^^ Invalid command: gif

Error: parse error

Perhaps it could be allowed? (Of course, adding an alpha character to the path works.)

[maaslalani]

Hey, thanks for the issue, I think this is reasonable. We should support any legal file name, in my opinion!

[maaslalani]

Just as a heads up this is valid for VHS:

Output "1.gif"

(notice the quotes)

[abhijit-hota]

@maaslalani Have opened a PR to address this: #108