Show contents page in doxygen.

Added links to link markdown pages in contents section. Adjusted
`DoxygenLayout.xml` tp show contents page.

Author: andreasfertig

CODE_OF_CONDUCT.md

@@ -1,4 +1,4 @@
-# Contributor Covenant Code of Conduct
+# Contributor Covenant Code of Conduct {#code_of_conduct}
 
 C++ Insights contributor covenant Code of Conduct.
 

CONTRIBUTING.md

@@ -1,4 +1,4 @@
-# Contributing to C++ Insights
+# Contributing to C++ Insights {#contributing}
 
 Thanks for considering contributing to **C++ Insights**.
 

Readme_Windows.md

@@ -1,4 +1,4 @@
-## Building on Windows
+## Building on Windows {#building_on_windows}
 
 ### Tested with (supported compilers)
 

TODO.md

@@ -1,4 +1,4 @@
-# C++ Insights ToDo
+# C++ Insights ToDo {#todo}
 
 This is a list of things I plan to do. If you like to jump in that's great. Please have a look at the [Code of Conduct](CODE_OF_CONDUCT.md) and [Contributing](CONTRIBUTING.md) before starting.
 

docs/Contents.md

@@ -0,0 +1,21 @@
+# Contents {#contents}
+
+Welcome to the C++ Insights project. Here you find some additional information about how to use C++ Insights,
+limitations, examples or how to contribute.
+
+In case, you don't know, you can try out C++ Insights online at [cppinsights.io](https://cppinsights.io). The source
+code can be found on [GitHub](https://github.com) at [github.com/andreasfertig/cppinsights](https://github.com/andreasfertig/cppinsights).
+
+##Resources
+
+* [Code of Conduct](@ref code_of_conduct)
+* [Contributing to C++ Insights ](@ref contributing)
+* [C++ Insights Command Line Options](@ref command_line_options)
+* [ToDo](@ref todo)
+* [Tests](@ref tests)
+
+##Readme's
+
+* [Readme Docs](@ref readme_docs)
+* [Readme Scripts](@ref readme_scripts)
+

docs/DoxygenLayout.xml

@@ -3,6 +3,7 @@
   <!-- Navigation index tabs for HTML output -->
   <navindex>
     <tab type="mainpage" visible="no" title=""/>
+    <tab type="user" url="@ref contents" title="Contents"/>
     <tab type="pages" visible="no" title="" intro=""/>
     <tab type="modules" visible="yes" title="" intro=""/>
     <tab type="classes" visible="yes" title="">

docs/Readme.md

@@ -1,8 +1,28 @@
-# C++ Insights - docs
+# C++ Insights - docs {#readme_docs}
 
-Configuration file for [doxygen](http://doxygen.org). The documentation can be created with cmake:
+This folder contains files used to generate the documentation which is available at
+[docs.cppinsights.io](https://docs.cppinsights.io). [Doxygen](http://doxygen.org) is used to generate the documentation.
+
+The documentation can be created with `cmake`:
 
 ```
 cmake --build . --target doc
 ```
 
+There are some pre- and post-processing steps involved.
+
+### Pre-processing
+
+1. `OptionDocumentationGenerator.cpp` is compiled and executed. It parses `InsightsOptions.def` to generate a list of all
+C++ Insights options including the help text and the default. For each option there must be a example C++ file in
+`examples`. This file is included in help.
+2. `OptionDocumentationGenerator.py` uses the previously generated markdown files and execute the C++ Insights binary
+   for each sample source file and includes the transformation result in the help file as well.
+
+### Post-processing
+
+Post-processing is done by `postProcessDoxygen.py`:
+
+1. Add `target="_blank"` for each external link in the generated HTML output.
+2. Remove unnecessary HTML files. For example, for each markdown file a File Reference file is created but empty.
+3. For the remaining HTML files generate a `sitemap.xml` such that search engines can index [docs.cppinsights.io](https://docs.cppinsights.io) properly.

scripts/Readme.md

@@ -1,3 +1,3 @@
-# C++ Insights - scripts
+# C++ Insights - scripts {#readme_scripts}
 
 This folder mostly hosts scripts for Travis CI builds.