update changelog for 2.0 release

CHANGELOG.md

@@ -1,6 +1,23 @@
+# 2.0
+
+ - Add no\_std support
+ - Bump MSRV to 1.67
+ - Refactor API to prevent direct modification and access of elements and to
+   allow access to the optional rfc1421-described headers.
+
+# 1.1.1
+ - Allow PEM files to be parsed with the optional rfc1421-described headers
+   (although you cannot retrieve the headers)
+
+# 1.1.0
+ - Add optional serde support
+
+# 1.0.2
+ - Remove dependency on Regex in favor of a hand-rolled parser
+
 # 1.0.1
 
- - hide the ASCII_ARMOR symbol to work around a linking issue with 32-bit windows builds
+ - hide the ASCII\_ARMOR symbol to work around a linking issue with 32-bit windows builds
 
 # 1.0