DOC: cache: update sections and fix some typos

Cache sections were not defined as the others, preventing them to be
correctly parsed by the HTML converter. Also, the "Cache" subsections
where not added to the summary.

This patch should be backported to the 1.8 branch.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index d71ba30..36a904e 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -109,6 +109,10 @@
 9.3.      Stream Processing Offload Engine (SPOE)
 
 10.   Cache
+10.1. Limitation
+10.2. Setup
+10.2.1. Cache section
+10.2.2. Proxy section
 
 1. Quick reminder about HTTP
 ----------------------------
@@ -16990,13 +16994,13 @@
 RAM.
 
 The cache is based on a memory which is shared between processes and threads,
-this memory is splitted in blocks of 1k.
+this memory is split in blocks of 1k.
 
 If an object is not used anymore, it can be deleted to store a new object
 independently of its expiration date. The oldest objects are deleted first
 when we try to allocate a new one.
 
-The cache use a hash of the host header and the URI as the key.
+The cache uses a hash of the host header and the URI as the key.
 
 It's possible to view the status of a cache using the Unix socket command
 "show cache" consult section 9.3 "Unix Socket commands" of Management Guide
@@ -17005,8 +17009,8 @@
 When an object is delivered from the cache, the server name in the log is
 replaced by "<CACHE>".
 
-10.1 Limitation
----------------
+10.1. Limitation
+----------------
 
 The cache won't store and won't deliver objects in these cases:
 
@@ -17022,16 +17026,16 @@
 
 Caution!: Due to the current limitation of the filters, it is not recommended
 to use the cache with other filters. Using them can cause undefined behavior
-if they modify the response (compression for exemple).
+if they modify the response (compression for example).
 
-10.2 Setup
-----------
+10.2. Setup
+-----------
 
 To setup a cache, you must define a cache section and use it in a proxy with
 the corresponding http-request and response actions.
 
-10.2.1 Cache section
---------------------
+10.2.1. Cache section
+---------------------
 
 cache <name>
   Declare a cache section, allocate a shared cache memory named <name>, the
@@ -17048,8 +17052,8 @@
   seconds, which means that you can't cache an object more than 60 seconds by
   default.
 
-10.2.2 Proxy section
---------------------
+10.2.2. Proxy section
+---------------------
 
 http-request cache-use <name>
   Try to deliver a cached object from the cache <name>. This directive is also