Plots 2D DXF file in current axes/figure (or creates a new figure/axes if none exist).

USAGE: dxf = DXFtool('filename.dxf')
INPUT: filename of dxf file as a string (may also include path).
OUTPUT: dxf object (optional).

FEATURES:
- supports: LINE, POINT, ARC, CIRCLE, ELLIPSE, LWPOLYLINE
- colored entities (line and hatch color)
- respects ordering of objects (back to front)
- supports bulges, open/closed polygons
- line dashing

TODO:
- more entities: DIMENSION, 3D stuff.
- improve handling of splines (currently piecewise linear)
- implement line weight handling

EXAMPLES:
1) Showing the possibilities
2) Using DXFplot to generate graphical legend
3) Importing and plotting CAD model from SolidWorks