0.2.0: Performance and improved ergonomics

• New Feature Implement own derived-value that can be disposed, which will remove watches on sources (atoms or other watchable things) PR #2

• New Feature Extend Rum drv mixin to accept multiple arguments PR #5 & PR #8.
  Previously you called d/drv multiple times:

    (rum/defcs block < rum/reactive (d/drv :product/page) (d/drv :product/images) (d/drv :product/text) 
      [state]
      (let [page (d/react state :product/page)
            images (d/react state :product/images)
            text (d/react state :product/text)] 
        ...))

  Now it is possible to pass multiple keywords to the same function
  with the same result as multiple invocations. Also there is a new
  function react-all that can be used to dereference multiple or all
  known derivatives at once:

    (rum/defcs block < rum/reactive (d/drv :product/page :product/images :product/text)
      [state]
      (let [{:keys [:product/text]} (d/react-all state)]
        [:p text] ,,,))

    (d/react-all state) -> {:product/page 'val :product/images 'val :product/text 'val}
    (d/react-all state :product/page) -> {:product/page 'val}

• Internal The sync-derivatives! function and the
  DerivativesPool constructor now receive an extra argument
  watch-key-prefix that helps avoiding conflicts when creating
  multiple pools from a single source atom with specs that have
  overlapping keys. See
  #10 for
  details.

• Bugfix Fix wrong assumption in tests that would cause them to fail when a spec
  contains more complex keys: 37cda80

• Bugfix Fix issue where sync-derivatives! would fail if spec keys don't implement IFn b5f9545