Closes i-RIC/iriclib#69

[kskinoue0612]

This adds the following functions, and *_mul versions:

• int cg_iRIC_Write_Sol_ParticleGroup_GroupBegin(const char* name)
• int cg_iRIC_Write_Sol_ParticleGroup_GroupEnd()
• int cg_iRIC_Write_Sol_ParticleGroup_Pos2d(double x, double y)
• int cg_iRIC_Write_Sol_ParticleGroup_Pos3d(double x, double y, double z)
• int cg_iRIC_Write_Sol_ParticleGroup_Integer(const char* name, int value)
• int cg_iRIC_Write_Sol_ParticleGroup_Real(const char* name, double value)