* Started with the most complicated game first.
* Struct made up of fixedhoriz class units.
* Append currently outgoing function names with `2` at the end to avoid conflict.
* For Duke/SW, we continually apply `SB_CENTERVIEW` only if it was previously a toggled action, similar to Blood.
* For SW, we remove two SW-specific bits (`PF_LOCK_HORIZ` and `PF_LOOKING`) that are no longer needed.
* For Duke, we remove `return_to_center` and just use the `SB_CENTERVIEW` action bit as required.
* For `sethorizon()`, feature set and adjustment speeds are an averaged out accumulation across Duke/SW:
** GameTicRate is factored in for adjustment decisions to provide consistency for SW being the faster game.
** Adjustment amounts are half way between Duke/SW.
* Remove fix16.h/cpp and utilise library from m_fixed.h.
* Extend m_fixed.h with two inline functions for int to/from float operations.
* Replace fix16_floor operations with those from xs_Float.h
* Replace multiple Q16.16 conversions from 0 to just be 0.
* Replaced all found in-game bit-shifts and multiplications/divisions with inline functions from m_fixed.h
* Replaced many casts of FRACUNIT as double in SW's panel.cpp as it is converted to double by way of type promotion.
* Fixed missed precision fixes in SW's panel.cpp where some types weren't declared correctly.
* Replaced 100+ `Cos()/Sin() >> 16` operations for Blood with inline functions `CosScale16()/SinScale16()`.
In particular this means to remove the option to disable widescreen aspect ratios. The way this was handled makes no sense with the current render backend.
The aspect ratio code will have to be redone entirely to properly obey the backend's settings.
