v3.1.0

• splash calc lightcurve implemented
• sink particles ON by default
• changing units rescales plot limits correctly
• further improvements to ray tracing / opacity rendering with physical opacity
• can change units temporarily without writing .units file
• auto-select closest velocity and mass unit and better default time unit in phantom/sphNG read
• error message if Inf or NaN read from .units file
• bug fix with units prompt
• floating colour bars are white not black
• automatically write copyright in Hollywood mode
• auto-render fits files
• read softening length from phantom sinks if accretion radius is zero;