Added cget command to pixBuf objects

Just implemented the cget command for pixBufs. It usage takes the form:

     pixBuf-id cget [-option]

These being the options that can be queried.

     -bitsPerSample
     -colorSpace   
     -hasAlpha
     -height
     -nChannels
     -pixels
     -rowStride
     -width

These correspond to the GdkPixBuf ‘ properties’ as described in the docs. A further option

     -key

is taken from the library docs relating to the function that ‘get’ the values of these properties. Semantically, if there is a cget, then ought to be a configure equivalent. Also, a new buffer should also be created using the familiar syntax.

     gnocl::pixBuf -width 100 -height 100 -bitsPerSample 8 -hasAlpha 1

Currently, this is initiated with:
    
     gnocl::pixBuf new width height depth

This is clearly inconsistent with the required syntax. This needs to be recoded.Of the options, I’m still not certain in my min d what the options actually - pixels and -key do. But, I’m sure all will be clear, or at least less confusing with time.