markdown sectins
add md fileending
reordering and embeded links
small changes
smaller titels
fix code indents
Add old README file back for bundling in packages. README.md can be developer oriented.
Update README.md to be more developer oriented.
Fix links and formatting.
Fix links, punctuation.
Social media.
Remove reference to 'mixxx' directory. Add libchromaprint to dependency list.
Use new Facebook page link.
Fix version/branch reporting.

* Include build.h in dlgabout.cpp
* Call MixxxApp::logBuildDetails() in MixxxApp constructor.
Fix tests.