fix build

Issue: #89
zero-initialize all floats
add simple matrix operations impl
use simple-mat now opencv nixed from core
revert centering changes
nix warn
evdev: avoid division by zero
evdev: prevent hang on exit with no events
remove libevdev tracker

Issue: #75
disconnect libevdev tracker from build

Issue: #75
revert freepie apk change for now
fix typo
use quaternions for centering

@KyokushinPL says was the only version that worked. Let's give it a try.

Goddamn issue: #63
separate config directory for 2.3-branch
reword cache variable comments
disconnect ftclient from build, sources remain
rename pose widget subdir
use zips, since github form insists
update binary release location
[ANN] core changes 2.2 -> 2.3

Following changes previously undocumented:

- Mapping now defaults to 0:180 if empty, no more empty mappings.
- Changes apply before clicking OK. Pressing Cancel cancels the changes.
- User interface got reorganized to be more compact.
- Can minimize to tray and start to tray in "keybindings" dialog.
- Can remap or disable axis from mapping -> options window.

- PT tracker lost its "dynamic pose resolution" functionality.
- Aruco tracker various improvements.
- FreePIE Android receiver added.
- Accela filter user-facing options changed to be more useful.
- Kalman and EWMA filters were improved.
- Octopus was fed.

-sh