Repr code and api rough edge smoothing.

[tatarize]

• EmbMatrix, EmbPattern, should have proper__repr__ code.
• The EmbPattern() repr should use the stitch command constants rather than the number values.
• EmbPattern *= EmbMatrix should transform the pattern by that matrix.
• There may be some utility to be gained by porting in the Matrix code from svgelements to replace the EmbMatrix. It would make the matrix highly similar to Pillow's needed matrix code form and SVGs. And would get all the fancy code things I worked in there like using matrixible strings.
• EmbPattern() should work, in part, as an interface bit of code for loading and saving filenames. (EmbPattern('my_embroidery.dst') * 'scale(2)').write('my_convertedembroidery.vp3')

With a proper *args, **kwargs erasure for EmbPattern the example write code:

from pyembroidery import *
pattern = EmbPattern()
pattern.add_block([(0, 0), (0, 100), (100, 100), (100, 0), (0, 0)], "red")
write_dst(pattern, "file.dst")

Could easily become.

from pyembroidery import *
pattern = EmbPattern([(0, 0), (0, 100), (100, 100), (100, 0), (0, 0)], "red").write('file.dst')

None of this would need breaking changes.