Change tag name subsection code to 11 (WebAssembly#213)

Name subsectsection code 3~9 are taken by the extended name section
proposal, and code 10 is taken by the GC proposal.

Fixes WebAssembly#211.

Author: aheejin

document/core/appendix/custom.rst

@@ -60,6 +60,7 @@ Id  Subsection
  0  :ref:`module name <binary-modulenamesec>`
  1  :ref:`function names <binary-funcnamesec>`    
  2  :ref:`local names <binary-localnamesec>`
+11  :ref:`tag names <binary-tagnamesec>`
 ==  ===========================================
 
 Each subsection may occur at most once, and in order of increasing id.

proposals/exception-handling/Exceptions.md

@@ -633,7 +633,7 @@ follows:
 | --------- | ---- | ----------- |
 | [Function](#function-names) | `1` | Assigns names to functions |
 | [Local](#local-names) | `2` | Assigns names to locals in functions |
-| [Tag](#tag-names) | `3` | Assigns names to tag types |
+| [Tag](#tag-names) | `11` | Assigns names to tags |
 
 ###### Tag names