Update PP_NUMBER regex definition

The previous regex escaped the digit separator ' as \' -
necessary only because the string itself was '' single-quoted.

This commit switches to use double-quote "" for the string
and removes the now unneeded escape.

Author: willwray

pcpp/parser.py

@@ -113,7 +113,7 @@ def t_CPP_LINECONT(t):
 
 # Preprocessor number
 def PP_NUMBER(t):
-    r'\.?\d(\.|[\w_]|\'[\w_]|[eEpP][-+])*'
+    r"\.?\d(?:\.|[\w_]|'[\w_]|[eEpP][-+])*"
     return t
 
 t_PP_NUMBER = PP_NUMBER