[build] Updates git ignore files
Removes internal list of command queues from GoclContext
Improves code in run_in_device() and run_in_device_sync() of GoclKernel
Changes type of @len argument in gocl_event_list_to_array() to guint

instead of gsize.
Adds new private method set_event_wait_list() to GoclEvent
Improves implementation of then() method in GoclEvent
Associates event wait list with event generated by run_in_device() of GoclKernel
Adds new method read() to GoclBuffer, for asynchronous reading from buffer
Removes unnecessary include of 'gocl-device.h' in GoclQueue
Fixes indentation in GoclDevice header file
[doc] Updates documenatation of GoclBuffer to include new method read()
Improve internal implementation of GoclEvent

Use clSetEventCallback, OpenCL user events and implements thread safety.
Adds new method has_extension() to GoclDevice
[doc] Adds documentation to has_extension() method of GoclDevice
Adds new method write() to GoclBuffer, for asynchronous writing to buffer