Release 0.7.5 UNDERLAY

[Manfred Moitzi]

• NEW: Drawing.acad_release property - AutoCAD release number for the drawing DXF version like ‘R12’ or ‘R2000’
• NEW: support for PDFUNDERLAY, DWFUNDERLAY and DGNUNDERLAY entities
• BUGFIX: fixed broken layout setup in repair routine
• BUGFIX: support for utf-8 encoding on saving, DXF R2007 and newer is saved with UTF-8 encoding
• CHANGE: Drawing.add_image_def(filename, size_in_pixel, name=None), renamed key to name and set name=None for auto-generated internal image name
• CHANGE: argument order of Layout.add_image(image_def, insert, size_in_units, rotation=0., dxfattribs=None)