[core] Refactor engine

This is going to be a bit more comprehensive than anticipated. In order
to cleanly refactor the core and the engine, basically start from
scratch with the implementation.

Goals:

* Test coverage
* Maintain backwards compatibility with module interface as much as
  possible (but still make modules easier to code)
* Simplicity

see #23

bin/customupdates

@@ -1,21 +0,0 @@
-#!/usr/bin/bash
-if ! type -P fakeroot >/dev/null; then
-	error 'Cannot find the fakeroot binary.'
-	exit 1
-fi
-
-if [[ -z $CHECKUPDATES_DB ]]; then
-	CHECKUPDATES_DB="${TMPDIR:-/tmp}/checkup-db-${USER}/"
-fi
-
-trap 'rm -f $CHECKUPDATES_DB/db.lck' INT TERM EXIT
-
-DBPath="${DBPath:-/var/lib/pacman/}"
-eval $(awk -F' *= *' '$1 ~ /DBPath/ { print $1 "=" $2 }' /etc/pacman.conf)
-
-mkdir -p "$CHECKUPDATES_DB"
-ln -s "${DBPath}/local" "$CHECKUPDATES_DB" &> /dev/null
-fakeroot -- pacman -Sy --dbpath "$CHECKUPDATES_DB" --logfile /dev/null &> /dev/null
-fakeroot pacman -Su -p --dbpath "$CHECKUPDATES_DB"
-
-exit 0

bin/load-i3-bars.sh

@@ -1,26 +0,0 @@
-#!/usr/bin/env bash
-
-if [ ! -f ~/.i3/config.template ]; then
-	cp ~/.i3/config ~/.i3/config.template
-else
-	cp ~/.i3/config.template ~/.i3/config
-fi
-
-screens=$(xrandr -q|grep ' connected'| grep -P '\d+x\d+' |cut -d' ' -f1)
-
-echo "screens: $screens"
-
-while read -r line; do
-	screen=$(echo $line | cut -d' ' -f1)
-	others=$(echo $screens|tr ' ' '\n'|grep -v $screen|tr '\n' '-'|sed 's/.$//')
-
-	if [ -f ~/.i3/config.$screen-$others ]; then
-		cat ~/.i3/config.$screen-$others >> ~/.i3/config
-	else
-		if [ -f ~/.i3/config.$screen ]; then
-			cat ~/.i3/config.$screen >> ~/.i3/config
-		fi
-	fi
-done <<< "$screens"
-
-i3-msg restart

bin/toggle-display.sh

@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-
-echo $(dirname $(readlink -f "$0"))
-
-i3bar_update=$(dirname $(readlink -f "$0"))/load-i3-bars.sh
-
-xrandr "$@"
-
-if [ -f $i3bar_update ]; then
-	sleep 1
-	$i3bar_update
-fi