changing the codecoveragethreshold to 80 as default module gets 83% only

…n has no parameter.

I'm now leveraging a feature from InvokeBuild to improve on the formatting done by InvokeBuild.

It now uses a header using the [`Set-BuildHeader`](https://github.com/nightroman/Invoke-Build/tree/master/Tasks/Header).
The default allows coloured output of task and display Task Name, synopsis, Task path, and task file.
See this [Appveyor build log](https://ci.appveyor.com/project/gaelcolas/samplemodule/build/1.0.141).
```
==============================================================================
			SET BUILD ENVIRONMENT VARIABLES
Using Build Helpers to Set default environment variables
-------------------------------------------------------------------------------
  /./Set_Build_Environment_Variables
  C:\projects\samplemodule\.build\BuildHelpers\Environment.BuildHelpers.build.ps1:10
...
Done /./Set_Build_Environment_Variables 00:00:00.2187430
===============================================================================
```

There is also an improved output in the PS Script Analyser Pester tests, to display the Message and Line when a rule is matched.