Add Doxygen configuration

[coderkun]

Based on @georgkrause’s Doxygen configuration this PR introduces a configuration file for Doxygen which generates a documentation in the folder ´doc´ and docstrings for some/many/all classes and methods (see #214).

To generate the documentation, simply run

$ doxygen Doxyfile

[georgkrause]

Works fine here. No we need some docstrings. Lets talk on IRC tomorrow, i would like to start on some midi stuff because i want to spend some time there.

[georgkrause]

lets merge this and add comments in new PRs

[harryhaaren]

@coderkun were the defaults of Doxygen used, or any particular config options changed? Anything special? Reviewing 2000+ lines isn't a good use of time :)

[georgkrause]

i generated it. I used a config which generates a lot of useful graphs (at least from my point of view).

• class hirarchy diagrams
• function call graphs

I used it in the first place to get the connections of the different parts of luppp without clicking through a lot if files.

Downside is, that it takes some time to compile.

[georgkrause]

In detail, i checked:

• Use dot tool from the GraphViz package
• Generate class diagrams
• Generate collaboration diagrams
• Generate overall class hierarchy
• Generate Include dependency graphs
• Generate Included by dependency graphs
• Generate call graphs
• Generate called by graphs

[coderkun]

Baset on @georgkrause, I set the README.md file as “main” file so that we have a nice description as start page of the documentation.

Thanks for merging!