Fixed inconsistency in chapter names

Some chapter titles included the chapter # and others didn't. All chapter #s removed from files (they remain in filenames).

3. Coexistence with Legacy IPv4/3. Coexistence with Legacy IPv4.md

@@ -1,4 +1,4 @@
-# 3. Coexistence with Legacy IPv4
+# Coexistence with Legacy IPv4
 
 The notion of a utopian IPv6-only world is a noble goal. However, as
 with any tectonic change, it happens slowly, and differing elements

4. Security/4. Security.md

@@ -1,4 +1,4 @@
-# 4. Security
+# Security
 
 Security has ever-growing importance in general and the IP protocol has
 been a big area for security research and development. The majority of

5. Network Design/5. Network Design.md

@@ -1,4 +1,4 @@
-# 5. Network Design
+# Network Design
 
 A first very general remark is that since IPv6 is a datagram protocol,
 whose routing relies on longest matching of address prefixes, the

99. Chapter Template/99. Chapter Template.md

@@ -1,4 +1,4 @@
-# 99. Chapter Template
+# Chapter Template
 
 This chapter shows how to write a new chapter. It is intentionally
 listed in the contents of the book itself, and is intended to be a
@@ -21,10 +21,10 @@ file with the same name again, e.g. `99. Chapter Template.md`.
 The first line in this file is:
 
 ```
-  # 99. Chapter Template
+  # Chapter Template
 ```
 
-so that makes three repetitions of `99. Chapter Template`.
+so that makes three repetitions of `Chapter Template`.
 
 Start with the general intro for a chapter. Tell the reader what the
 chapter is all about. Then give a list of the sections. It would be