Update indentation in reference

doc/system/reference.adoc

@@ -314,10 +314,10 @@ namespace boost {
 private:
 
     unsigned long long id_; // exposition only
-
 };
-  }
-}
+
+} // namespace system
+} // namespace boost
 ```
 
 #### Constructors
@@ -427,12 +427,16 @@ const char* my_category::message(int ev, char* buffer, size_t len) const noexcep
     case 0: return "no error";
     case 1: return "voltage out of range";
     case 2: return "impedance mismatch";
+
     case 31:
     case 32:
     case 33:
+
         std::snprintf(buffer, len, "component %d failure", ev-30);
         return buffer;
+
     default:
+
         std::snprintf(buffer, len, "unknown error %d", ev);
         return buffer;
     }
@@ -559,7 +563,7 @@ namespace boost {
 class error_code {
 public:
 
-      // constructors:
+    // constructors
 
     constexpr error_code() noexcept;
     constexpr error_code( int val, const error_category & cat ) noexcept;
@@ -572,7 +576,7 @@ namespace boost {
 
     error_code( std::error_code const& ec ) noexcept;
 
-      // modifiers:
+    // modifiers
 
     constexpr void assign( int val, const error_category & cat ) noexcept;
 
@@ -584,7 +588,7 @@ namespace boost {
 
     constexpr void clear() noexcept;
 
-      // observers:
+    // observers
 
     constexpr int value() const noexcept;
     constexpr const error_category & category() const noexcept;
@@ -600,7 +604,7 @@ namespace boost {
     bool has_location() const noexcept;
     boost::source_location const & location() const noexcept;
 
-      // comparisons:
+    // comparisons
 
     friend constexpr bool operator==( const error_code & lhs,
       const error_code & rhs ) noexcept;
@@ -641,7 +645,7 @@ namespace boost {
     template<class E>
       friend constexpr bool operator!=( E lhs, const error_code & rhs ) noexcept;
 
-      // conversions:
+    // conversions
 
     operator std::error_code() const;
     operator std::error_code();
@@ -651,10 +655,10 @@ namespace boost {
 
     std::string to_string() const;
 
-      // stream insertion:
+    // stream insertion
 
     template <class charT, class traits>
-        std::basic_ostream<charT, traits>&
+      friend std::basic_ostream<charT, traits>&
         operator<<( basic_ostream<charT, traits>& os, const error_code & ec );
 };
 
@@ -662,8 +666,8 @@ namespace boost {
 
 std::size_t hash_value( const error_code & ec );
 
-  }
-}
+} // namespace system
+} // namespace boost
 ```
 
 #### Constructors
@@ -1039,7 +1043,7 @@ namespace boost {
 class error_condition {
 public:
 
-      // constructors:
+    // constructors
 
     constexpr error_condition() noexcept;
     constexpr error_condition( int val, const error_category & cat ) noexcept;
@@ -1047,7 +1051,7 @@ namespace boost {
     template <class ErrorConditionEnum>
       constexpr error_condition( ErrorConditionEnum e ) noexcept;
 
-      // modifiers:
+    // modifiers
 
     constexpr void assign( int val, const error_category & cat ) noexcept;
 
@@ -1056,7 +1060,7 @@ namespace boost {
 
     constexpr void clear() noexcept;
 
-      // observers:
+    // observers
 
     constexpr int value() const noexcept;
     constexpr const error_category & category() const noexcept;
@@ -1067,7 +1071,7 @@ namespace boost {
     constexpr bool failed() const noexcept;
     constexpr explicit operator bool() const noexcept;
 
-      // comparisons:
+    // comparisons
 
     friend constexpr bool operator==( const error_condition & lhs,
       const error_condition & rhs ) noexcept;
@@ -1088,18 +1092,19 @@ namespace boost {
     friend bool operator!=( const error_condition & condition,
       const std::error_code & code ) noexcept;
 
-      // conversions:
+    // conversions
 
     operator std::error_condition() const;
 
-      // stream insertion:
+    // stream insertion
 
     template <class charT, class traits>
-        std::basic_ostream<charT, traits>&
+      friend std::basic_ostream<charT, traits>&
         operator<<( basic_ostream<charT, traits>& os, const error_condition & en );
 };
-  }
-}
+
+} // namespace system
+} // namespace boost
 ```
 
 #### Constructors
@@ -1295,7 +1300,7 @@ Returns: ::
 
 ## <boost/system/{zwsp}system_error.hpp>
 
-### Class system_error
+### system_error
 
 The class `system_error` describes an exception object used to
 report errors that have an associated `error_code`. Such errors
@@ -1303,10 +1308,9 @@ typically originate from operating system or other low-level
 application program interfaces.
 
 ```
-namespace boost
-{
-  namespace system
-  {
+namespace boost {
+namespace system {
+
 class system_error: public std::runtime_error
 {
 public:
@@ -1324,8 +1328,9 @@ namespace boost
     error_code code() const noexcept;
     const char * what() const noexcept;
 };
-  }
-}
+
+} // namespace system
+} // namespace boost
 ```
 
 #### Constructors