Add Bitmap caching support

[openaphid]

Bitmap instances are constantly created and recycled during flipping.

Implementing a bitmap cache could improve performance and reduce the risk of OOM errors.

[VAdaihiep]

I think if the screenshot already recycle before created new screenshot, the memory can not be out when flip many time because it's de-allocate after recycle(). I mean maybe created and recycle bitmap is not the reason of OOM error, maybe the reason is: Somethings goes bigger after each flipping -> OOM errors.

[openaphid]

The issue is about to reduce the risk, not to avoid it.

I analyzed the heap status after flipping 100+ pages. There is no bitmap instances or other objects leaking. Then I thought OOM is caused by the behavior of adapter.

Please refer to #33, I will push a fix in a minute

[openaphid]

Leave it close as the memory leak has been identified in #33