Introduce `ASTableView`, a UITableView subclass that uses `ASCellNode`
instead of UITableViewCell. Add working range support via
`ASRangeController`, which observes the visible range, maintains a
working range, and handles most ASDK machinery. ASRangeController is
loosely-enough coupled that it should be easily adapted to
UICollectionView if that's desired in the future.
Notable considerations in the ASRangeController architecture:
* There's no sense rewriting UITableView -- the real win comes from
using nodes instead of UITableViewCells (easily parallelisable
computation, large number of cells vs. few table views, etc.). So,
use a UITableView with empty cells, using UITableViewCell's
contentView as a host for arbitrary node hierarchies.
* Instead of lazy-loading cells the instant they're needed by
UITableView, load them in advance. Preload a substantial number of
nodes in the direction of scroll, as well as a small buffer in the
other direction.
* Maintain compatibility with UITableView's API, with one primary change
-- consumer code yields configured ASCellNodes, not UITableViewCells.
* Don't use -tableView:heightForRowAtIndexPath:. Nodes already compute
their preferred sizes and cache results for use at layout-time, so
ASTableView uses their calculatedSizes directly.
* Corollary: ASTableView is only aware of nodes that have been sized.
This means that, if a cell appears onscreen, it has layout data and
can display a "realistic placeholder", e.g. by making its subnodes'
background colour grey.
Other improvements:
* Remove dead references and update headers (fixes#7, #20).
* Rename `-[ASDisplayNode sizeToFit:]` to `-measure:` and fix
`constrainedSizeForCalulatedSize` typo (fixes#15).
* Rename `-willAppear` and `-didDisappear` to `-willEnterHierarchy` and
`-didExitHierarchy`. Remove `-willDisappear` -- it was redundant, and
there was no counterpart `-didAppear`.
* Rename `viewLoaded` to `nodeLoaded`.
Summary:
Import the headers for control, image, and text nodes, as well as the normal display node and helper functions. Subclass headers omitted as they are intended to be imported in subclass implementation files, not public headers.
Test Plan:
`#import <AsyncDisplayKit/AsyncDisplayKit.h>` followed some time later by:
```
ASDisplayNode *node;
ASImageNode *node2;
ASTextNode *node3;
ASControlNode *node4;
```
Summary:
* Moves ASThread.h from Private to Public visibility
* Moves ASThread.h from Private/ to Details/
* Changes public #imports from "" to <>
Test Plan:
```
#import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
#import <AsyncDisplayKit/ASControlNode+Subclasses.h>
```
