Fixing combination of level5(modifier_mapping) + ctrl(swap_lalt_lctrl)

The combination of level5(modifier_mapping) + ctrl(swap_lalt_lctrl) caused troubles, changing the way is interpreted. Please consult issue #266 (closed) for a full description of the problems observed.

This merge request is a full rewrite of Hyena layout.

The implementation was moved to symbols/hyena so that it avoids bloat and pollution in symbols/us and also allows the implementation to be employed easily in other languages too. So, at this point, we provide Hyena for symbols/us and symbols/gb.

One very important aspect of the implementation provided at symbols/hyena is that it is composable and agnostic about how it is being employed. This way, Hyena can be mixed and composed with some other existing layouts, making it easy to bring the benefits of Hyena on top of existing national layouts.

This merge request was fully tested for a couple of days and behaves as expected, not presenting any troubles to existing windowing environments and applications. As a side note, certain applications, like IntelliJ, make raw low level keyboard reads, not behaving very well in certain cases, but this is a problem specific to these kind of applications, which choose to read keyboard input at such low level.

I'm in the process of writing an external documentation which explains why this work was created and will soon provide pictures of the layouts provided. It is here: http://github.com/frgomes/hyena