sgo - Simple Geographical Operations (with OSGB36)

• Fixed: Now, when converting from 2D BNG to 3D BNG, the input is first converted
  to 3D by filling z with zeros. Previous versions just added zeros to the output.
• Fixed: When converting from 2D to 3D coordinates with the same datum the z
  column was not being filled with zeroes.
• Fixed: Points right on the upper boundaries of the OSTN grid are considered
  outside of the OSTN15 rectangle.
• Fixed: Output text of the print function.
• Improved slightly the speed of 3D calculations from/to BNG.
• Improved some parts of sgo_transforms's documentation.