Version 1.4.6

Changes in this version:

• Add function mean (or average) to compute the mean value of probability distributions (by haykam821). For example:

  > mean(d6)
  7
  > average(1d20 + 5)
  15.5
  

• Add units nibble (4 bits) and U (rack units, equal to 1.75 inches)
• Serialised variables are now compatible between 32-bit and 64-bit platforms
• Fix bug where calculating very large roman numerals could crash the application