Fixed name of Ascendant

it was typed consequently as “ascendent”
Fixed Makefile to install all header files as required
Removed unnecessary const prefix from GsweMoment methods returning boxed types
Bug fix in gswe_moment_calculate_antiscia()

antiscion_data->antiscion_axis_info can be NULL, but at that point
antiscion_data->antiscion_axis_info->axes can't be GSWE_ANTISCION_AXIS_NONE
Fixed GsweAntiscionAxisInfo API to comply with GsweAspectInfo API
Small performance fixes

Removed some unnecessary checks
Outsourced Moon phase calculation to GsweMoonPhaseData