This directory holds core functionality of FastLED.

Every class/struct/function in this directory must be under the
namespace fl, except for special cases.

This is done because according to the the Arduino build system,
all headers/cpp/hpp files in the root the src directory will be in global
scope and other libraries can #include them by mistake.

This has happened so many times that I've just gone ahead and migrated all
the new code to this directory, to prevent name collisions.

# When to put stuff in `fl` and not `fx`

If it's a visualizer, put it in the `fx` fodler. If it it's something to help to build a visualizer then you put it here.