added decimal note/rest lengths

[pzxwang]

For issue #16. I also allowed for decimal rest lengths since they are parsed similarly to note lengths.

Thank you for providing some low-hanging fruit for those of us just starting out.

To follow up, should expressing length in seconds also be allowed in decimals (e.g. 2.5s)? I think millisecond values have to be integers, though.
As for the set-note-length function discussed in the issue, I noticed that in the documentation you suggest just calling the note-length function inside set-duration. Would you still like to add set-note-length as a convenience function of sorts?

[daveyarwood]

Thanks for the PR! In general I think this looks good, I just have a couple of aesthetic nitpicks.

Re: lengths in seconds, I'd rather not allow those to be expressed with decimals, for the sake of simplicity. We do have millisecond lengths, and I don't think it's too cumbersome to enter 2500ms instead of 2.5s.

I would still like to add a set-note-length convenience function to alda.lisp; I think we could put it in alda.lisp.attributes below where set-duration is defined.

[daveyarwood]

In retrospect, I'm not sure why I had it nested like this in the first place:

  (testing "ties"
    (testing "ties"
      ...

Probably a silly error my part. I think we can remove a layer of nesting and just do this:

(deftest tie-and-slur-tests
  (testing "ties"
    ...)
  (testing "slurs"
    ...))

[daveyarwood]

Not sure if this was intentional, but could we back this change out, i.e. put the space back in?

[daveyarwood]

@pzxwang: Looks even better now, tests pass, and it looks like it's working as expected when I test it.

Excellent work, thank you! 👍