读取DXF文件和保存DXF文件,处理通用实体，并且加入了Polygon和Polyface的接口-his is not a　complete　DXF reader package, but it handles most

entities that are commonly found. With this release I ve added

the Polygon mesh and Polyface mesh varieties of POLYLINE, so a

great many of the 3D model DXF files found on the internet can now

be loaded and at least viewed in 2D. In addition, I ve implemented

the Arbitrary Axis Algorithm and associated 3D transformations

which allows general purpose 3D datasets to be loaded and viewed

in 2D. In addition to both the above points, BLOCKs are now

supported, but the fact that they (and other objects) can be

inserted in arbitrary positions and with 3D rotations added, has

complicated the drawing routines somewhat.