Restructure project files and "librify"

This adds two subdirectories and places the sources in there:

  examples/    - demonstrations and standalone applications
  pe/          - particle engine sources

The particle engine sources are compiled into a libpe.la library.
particle-swarm: Remove two unused func parameters
particle-swarm: Refactor and optimise global force
particle-swarm: Add missing break from switch case
particle-swarm: Document some obscure code
ants: Tweak demo properties
boids: Add a slight "current"
Replace boids -> fish
Specifically include GLib flags

Don't depend on Cogl pulling them in