Cleanup imports and add file-wide comments

src/filecheck.py

@@ -1,3 +1,5 @@
+# check that a file is creatable/writable/editable
+
 import os.path
 
 # check that a file can be edited

src/lattice.py

@@ -1,3 +1,5 @@
+# define background lattices
+
 from point import Point
 
 # parent class of all lattices

src/painter.py

@@ -1,3 +1,5 @@
+# main drawing class
+
 import sys
 import math
 from kivy.uix.widget import Widget

src/point.py

@@ -1,3 +1,5 @@
+# two-dimensional point structure
+
 import math
 
 # point in two dimensions