Added GHorizDir class to store alt/az coordinates
fixed some typos preventing compile
fixed prototype for zenith() and zenith_deg()
added GHorizDir to default includes
fixed incorrect #define at top of file
add small test case for GHorizDir
implemented basic loading and interpolation of pointing direction (needs work and testing)
use GTime in interpolation
fixed bug in pointing interpolation (now gives reasonable answers in test case)
Merge branch '1113-implement-altaz-pointing' into integration. Add Python interface for GHorizDir class and revise code.

Conflicts (resolved):
	inst/cta/include/GCTAPointing.hpp
	inst/cta/test/test_CTA.cpp
Clean up GCTAPointing code after integration of pointing table.

The code now handles properly time references, the pointing table file has been updated for this purpose. A load constructor has also been added that allows construction of a GCTAPointing object from a pointing table file.
Adjust unit test for new GCTAPointing
Correct allocation of lookup table.
Update documentation concerning CTA pointing tables.