Merge pull request #169 from ubick/develop

Colorize effect by sadlig
Merge pull request #170 from ubick/develop

Added usage documentation for the Grayscale effect.
Instantiate GD layers only when it is required
Merge pull request #174 from romainneutron/GDLayers

Instantiate GD layers only when it is required
Count layers, not `$this`.
`Imagine\Imagick\Image#save()` should count `$this->layers()`, not `$this`.
Imagick coalesces opened or read files.
Animated GIFs may contain inconsistently sized frames. Coalescing this frames makes sure all frames are of the same size.
Let Imagick write multiple, adjoined images
To allow for animated gifs, let Imagick write multiple, adjoined images.
Added `{@inheritdoc}` for `Imagine\Gd\Layers#merge()`.
Added `LayersInterface#coalesce()`.
Moved image coalescing from `Imagine\Imagick\Imagine` to `LayersInterface#coalesce()`.
`Imagine\Imagick\Layers` now throws Imagick exceptions.
`Imagine\Imagick\Layers` now throws Imagick instead of Gmagick exceptions.
Updated API docs accordingly.
Move exceptions thrown by Imagine::open to the Imagine scope
Catch exception in `Imagine\Imagick\Layer#coalesce()`.
Multi-layer support for `ImageInterface#get()`.
Multi-layer support for `Imagine\Gmagick\Image#get()`.
Removed stray `Gmagick#writeimage()` call.
Type check not needed in `Gmagick#get()` and `Imagick#get()`.
Camelcase in `Imagine\Imagick\Layers#coalesce()`.
Merge pull request #179 from romainneutron/OpenExceptions

Move exceptions thrown by Imagine::open to the Imagine scope
Moved exception handling to account for `writeImages()` et al.