Add CompoundLayout

[luigiberrettini]

As per issue #1543 I added a CompoundLayout Layout to make it possible to use multiple nested heterogeneous layouts and create complex log entries.

Take as an example the following configuration:

<nlog>
  <targets>
    <target name='file' type='File' fileName='log.txt'>
      <layout type='CompoundLayout'>
        <layout type='SimpleLayout' text="myAmazingText: " />
        <layout type='JsonLayout'>
          <attribute name='time' layout='${longdate}' />
          <attribute name='level' layout='${level:upperCase=true}'/>
          <attribute name='nested' encode='false'  >
            <layout type='JsonLayout'>
              <attribute name='message' layout='${message}' />
              <attribute name='exception' layout='${exception}' />
            </layout>
          </attribute>
        </layout>
      </layout>
    </target>
  </targets>
  <rules>
  </rules>
</nlog>

Log entries would be like this:

myAmazingText: { "time": "2016-10-30 13:30:55.0000", "level": "INFO", "nested": { "message": "this is message", "exception": "test" } }

[304NotModified]

\0/

[codecov-io]

Current coverage is 76% (diff: 87%)

Merging #1551 into master will increase coverage by <1%

@@             master      #1551   diff @@
==========================================
  Files           269        270     +1   
  Lines         16266      16293    +27   
  Methods        2605       2611     +6   
  Messages          0          0          
  Branches       1769       1771     +2   
==========================================
+ Hits          12367      12393    +26   
- Misses         3487       3501    +14   
+ Partials        412        399    -13   

Powered by Codecov. Last update 698ca65...ff95156

[304NotModified]

I think this is OK, but maybe nice to add some (XML) comments.

[304NotModified]

Looks good, added some notes!

[304NotModified]

Any idea if we could test this case:

(CreateArrayItemInstance returning null)
See https://codecov.io/gh/NLog/NLog/compare/698ca65c2ea8ac508a13f8d49d0e1c3c7a012c5c...f6d0d4a92c528cfd97927222847ac8b81ad0de87

[304NotModified]

I think we almost ready to merge this.

Can you add those on the wiki? Public is fine. Please add some examples and "introduced in NLog 4.3.6"

[luigiberrettini]

I just added the documentation.

https://github.com/NLog/NLog/wiki/Layouts
(I suppose the NuGet badge will auto-update to 4.3.6 when you release it)

https://github.com/NLog/NLog/wiki/CompoundLayout

[304NotModified]

Great! Thanks!

An yes, the badge works automatically :)

[304NotModified]

It's online!