Plane: Added getter methods for all Plane property values

Plus various refactorings to move more code into the class itself.
Merge branch 'master' into mapdata-c++
Vertex: Added getter methods for all Vertex property values

Plus various refactorings to move more code into the class itself.
Merge branch 'master' into mapdata-c++
Refactor|Vertex: Further API improvements for Vertex
Refactor|HEdge: Moved all HEdge_* functions to methods of HEdge
Vertex: Fixed oversight in the previous cleanup refactoring
Merge branch 'master' into mapdata-c++
Refactor|BspLeaf: Moved all BspLeaf_* functions to methods of BspLeaf
Refactor|BspNode: Moved all BspNode_* functions to methods of BspNode
Refactor|Sector: Moved all Sector_* functions to methods of Sector
Refactor|LineDef: Moved all LineDef_* functions to methods of LineDef
Refactor|SideDef: Moved all SideDef_* functions to methods of SideDef
BspLeaf: Added getter methods for all BspLeaf property values
Fix typo
Merge branch 'master' into mapdata-c++
BspNode: Added getter methods for all BspNode property values
Fix typos and added a @todo re BSP tree element types
Cleanup
Refactor|LineDef: Replaced various LineDef accessor/helper macros