Remove .md and image files and move python files into main chapter folders

thinkcspy/Chapter-9-Exercises/Problem11.py

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+# Runestone.Academy thinkcspy course
+# Chapter 9
+# Problem 11
+
+def remove(substr,theStr):
+    # your code here
+    pos1 = 0
+    pos2 = len(substr)
+    found = False
+    newStr = theStr
+    
+    while pos1 < len(newStr) and not found:
+        currentPos = newStr[pos1:pos2]
+        
+        if substr == currentPos:
+            newStr = newStr[:pos1] + newStr[pos2:]
+            found = True
+        else:
+            pos1 += 1
+            pos2 += 1
+    
+    return newStr
+
+print(remove("e", "tree"))
+print(remove("iss", "Mississippi"))
+print(remove("an", "banana"))
+print(remove("e", "treeeleee"))