v1.5: Implemented two new entries (TLE and SunMoon_model) in simulation par…

NOTE: two new entries (TLE and SunMoon_model) in simulation parameters XML and schema have been implemented. XML simulation parameters files of older versions have to be updated including the two new entries.
Implemented hardcoded version of gravity field model GGM03C 30x30, Harris-Priester atmospheric model, low precision solar coordinates functions.
Implementation of state transformation from ICRF to ITRF which does not rely on SPICE library but on internal libraries + IGS IGU data (erp files).
Fixed bug in Events.cpp (duration in seconds instead of minutes).
Updated SpOCK user manual.

v1.3

Added SGP4 propagator.

v1.2

Added simulation run status bar.

Added #define BOOST_BIND_GLOBAL_PLACEHOLDERS in Propagator.h and HIL_interface.cpp.
Explicit initialization of struct members of SYS_Parameters in Subsystem.cpp.
Fixed bug in orbit propulsion class for thrust resolution and execution of negative continuous maneuvers.
Implemented first version of Ctrl execution by orbit propulsion system in main file orbprop.cpp.
Implemented header option in I/O function read_csvfile.
Created variable type struct Pass.
Implemented generation of lists of GS, TG and GS + TG passes sorted by time for each spacecraft and all spacecraft.
Modified headers in events output files.
Updated Eigen, spice and xerces libraries. Implemented check and error message on duration of attitude propagation.
Updated environment and auxiliary files in data folder.
Updated user guide.

v1.0

First release