v0.13.5

Roentgen v0.13.5

Diff since v0.13.4

Merged pull requests:

• Kernel Truncation in reconstruct_dose (#85) (@lmejn)
• Fixed negative dose bug (#88) (@lmejn)
• Tidied IO code and added VTK Beamlet writer (#89) (@lmejn)

Closed issues:

• Some treatment plans cause very negative doses (#87)