Review GTime, GTimeReference, GGti, GEbounds and GPhoton classes.

GTime
  The secs() method now returns a const reference.

GTimeReference
  The load constructor and the read() and write() methods take
  a const reference instead of a pointer.

GGti
  The read() and write() methods now use references instead of
  pointers. The clobber argument in the save() method is passed
  as const reference.

GEbounds
  The read() and write() methods now use FITS references instead
  of pointers. The clobber argument in the save() method is passed
  as const reference.

GPhoton
  Add mcid argument to Photon constructor (defaults to -1).
The FITS read() and write() methods now take reference instead of pointers.
Adjust class documentation.
Review event container interface.

GEvents
GEventList
  The clobber argument of the save() method is now passed as const
  reference.

GEventCube
  The clobber argument of the save() method and the axis argument of the
  naxis() method are now passed as const references.
Review GObservation class.

The events() set method now takes a const reference instead of a const pointer as argument. Some methods have now been defined inline.
Remove GPointing class.

The abstract pointing class has been removed as so far no abstract pointing interface is needed.
GObservation::response() method now returns a const reference.
Implement GCTAResponse and GCTAPointing as members of GCTAObservation.

Before, response and pointing objects have been allocated dynamically. Now they are members of GCTAObservation.
Implement GLATResponse and GLATPointing as members of GLATObservation.
Implement GCOMPointing and GCOMRespose as class members.
Remove const at() method.
Review of GammaLib core code.

These are the final modifications for the GammaLib core code review.
Rename omega() methods to solidangle().

All methods returning a solid angle are now named solidangle().