rename inkstitch/ to lib/

You can't have a module and a package named the same thing.  PyInstaller wants
to import the main script as if it were a module, and this doesn't work unless
there's no directory of the same name with a __init__.py in it.

inkstitch.py

@@ -1,8 +1,8 @@
 import sys
 import traceback
 from argparse import ArgumentParser
-from inkstitch.utils import save_stderr, restore_stderr
-from inkstitch import extensions
+from lib.utils import save_stderr, restore_stderr
+from lib import extensions
 
 
 parser = ArgumentParser()

lib/__init__.py

@@ -7,8 +7,8 @@ import gettext
 from copy import deepcopy
 import math
 import libembroidery
-from inkstitch.utils import cache
-from inkstitch.utils.geometry import Point
+from .utils import cache
+from .utils.geometry import Point
 
 import inkex
 import simplepath