PNG Guides and EmbPattern init.

PngWriter has guides added.
A couple corrections to PngWriter.
PyEmbroidery is turned into a shell references to EmbPattern static calls.
EmbPattern has init parameters of filename, or EmbPattern.
EmbPattern has .read() and .write() which accept settings as direct keyword arguments.

pyembroidery/ArtReader.py

@@ -0,0 +1,30 @@
+# from .ReadHelper import read_int_8
+# from io import BytesIO
+#
+# import compoundfiles
+# import zlib
+#
+#
+# def swizzle(b):
+#     b ^= 0xD2
+#     b <<= 1
+#     b |= b >> 8
+#     return b & 0xFF
+#
+#
+# def parse_art_file(file):
+#     with open(file, 'rb') as f:
+#         contents = compoundfiles.CompoundFileReader(f).open('Contents')
+#         contents.seek(4)  # file size
+#         return zlib.decompress(bytes([swizzle(b) for b in contents.read()]))
+#
+#
+# def read(f, out, settings=None):
+#     contents = compoundfiles.CompoundFileReader(f).open('Contents')
+#     contents.seek(4)  # file size
+#     art = BytesIO(zlib.decompress(bytes([swizzle(b) for b in contents.read()])))
+#     while True:
+#         b = read_int_8(art)
+#         if b is None or b == -1:
+#             break
+#         print('%02X' % b)