v0.2.1-beta

• removed g_add()
• bugfixes regarding absolute E coords and splitting objects
• added list methods for Gcode to easily operate on them:
  • insert()
  • append()
  • extend()
  • __add__()
  • __len__()
• Gcode can be sliced with Gcode[x:y]

Full Changelog: v0.2.0-beta...v0.2.1-beta