Adds support for Scalr options

[brianium]

fixes #29

@mikera let me know if anything jumps out as wrong/improvable :)

Due to the multi-arity signatures of resize and scale I found it difficult to create a backwards compatible change that made sense. So a couple of options seemed viable to me:

1. Leave as is in the PR and options is now required (probably a major version change?)
2. Convert all arguments to entries in an options or params map - i.e :new-width, :new-height (probably a major version change?) Something like:

(scale img {:height 100 :width: 100 :method :ultra-quaity})

3. Something entirely different because I'm fairly certain I don't know everything 😄

Again, thanks a lot for this lib! Let me know what I can do to help get this PR merged 💯

[mikera]

Thanks @brianium ! I think the extra parameters would be better specified as an additional options map argument (keyword args are a bit fiddly to compose.

Could you make this modification then I'll merge and release? Thanks!

[brianium]

@mikera I think I may be a bit confused. I thought what I included in this PR was an options map (just destructured).

I just wasn't sure on how to include an optional options map and maintain backwards compatibility (if that is the goal) with the multi arity signatures of resize. So how should I include an optional options map for a function that can accept new-width and new-height and optionally options, as well as new-width and optionally options (how is this scenario distinguished from providing new-width and new-height)?

I'm finding this a bit difficult to articulate so I apologize in advance :)

The PR I submitted currently supports the following:

(resize ant 250 {:method :ultra-quality})

;; or

(resize ant 250 400 {:method :ultra-quality})

;; but how would we support the former syntaxes of no options and optionally no height?

(resize ant 250) ;;[img new-width]
(resize ant 250 400) ;; [img new-width new-height]

What if someone wants to invoke with just new-width and also pass options?

[brianium]

@mikera sorry if I made a confused mess 🙍‍♂️ - let me know if there is something I can do to keep this moving along - even if its scrap it and start over 😄

[yuhan0]

Another way of exposing this API could be through dynamic vars?
Something like:

(def ^{:dynamic true} *scaling-options*
  {:method :balanced, :mode :fit-exact})

And at the call site:

(binding [*scaling-options* {:method :ultra-quality}]
  (resize ant 250))