Move header files into include/midifile folder.

[no-more-secrets]

Effectively we add a folder "namespace" to the midifile headers.
This is standard practice when structuring a library (e.g. note
boost does this). When a parent project includes this library it
will be more clear which headers belong to the midifile
library.

Also a minor CMake fix is made which will associate the header
folder with the midifile CMake target in accordance with modern
CMake best practices.

These changes make the project more friendly to the common
workflow of incorporating the library into a larger project as a
git submodule.

Fixes #62

[no-more-secrets]

Ping!

[no-more-secrets]

Is this repo still being maintained?

[craigsapp]

I pay attention to the repo every January/February when I teach MIDI in my class :-)

You still find this useful (as a Windows user, while I am a unix/mac user)? As long as no one on the watch list complains, I will do it this week.

When I use the files in an external project, I just copy them into the include/src directories of the project. But otherwise, it seems that the directory structure midifile/include/midifile is a bit redundant.

[no-more-secrets]

When I use the files in an external project, I just copy them into the include/src directories of the project. But otherwise, it seems that the directory structure midifile/include/midifile is a bit redundant.

Note that when included from a C++ file it will be #include "midifile/..."; the "midifile/include" part is not visible since that is part of the header search paths. That's why it is not redundant from that point of view. This is a common practice in C++ library code bases.

Anyway, if you are planning to merge this, then please let me know so that I can update the branch and resolve the merge conflicts (which I don't want to do unless you're going to merge it). Thanks