zs_dxf v1.0.0

It is a fork of https://github.com/vagran/dxf-viewer. We need it to make some improvements over the original code:

• Support viewports
• Switch layouts
• Fixed some Insert Entity position rotation bugs

https://github.com/vagran/dxf-viewer is a fork of https://github.com/gdsestimating/dxf-parser, and make some improvements over the original code:

• Support additional DXF groups.
• Stream parsing - parse text as it is fetched without buffering. This allows parsing huge files with limited memory consumption.
• Result filtering - do not include data which is not needed on further processing steps, filtering it on-the-fly, thus minimizing memory consumption even more.
• Additional features support (e.g. hatching).