Use fr'..{var}...' to simplify creating regex strings (#429)

Using fr'....{var}...' makes for shorter and more readable string creation.

Now that TriBITS requires Python 3 (or at least it is only tested with Python
3), it is good to be able to start using these newer language features.

I tested this manaully locally and it seems to work correctly.

refactoring/token-replace.py

@@ -52,9 +52,9 @@ def getCmndLineOptions():
   inOptions = getCmndLineOptions()
 
   beginLineTokenPattern = re.compile(
-    r'^' + inOptions.tokenToReplace + r'([^A-Za-z0-9_])' )
+    fr'^{inOptions.tokenToReplace}([^A-Za-z0-9_])' )
   midLineTokenPattern = re.compile(
-    r'([^A-Za-z0-9_])' + inOptions.tokenToReplace + r'([^A-Za-z0-9_])' )
+    fr'([^A-Za-z0-9_]){inOptions.tokenToReplace}([^A-Za-z0-9_])' )
 
   with open(inOptions.inputFile, 'r') as file:
     lines = file.readlines()