Pre-alpha version 0.3 released

Implemented a page to display hi-scores. Access by clicking "see hi-scores" next to "reset hi-scores".
Implemented social buttons as Flattr, Twitter and Facebook, only meant to be displayed in the project page, hosted by Verticea.
Implemented an "overall" score, saved and beatable like every other statistic. Also displayed in the Hi-Score page. The Game-over screen is clearer this way.
Implemented the magnet shot going straight but attracted to asteroids, and leading to mine launcher, which shots are staying here waiting for an asteroid to come nearby and get attracted to it. This weapon has two modes : following the basic cannon and revolution, where the cannons are just going around.
Implemented hammer shot, leading to broom, both making the asteroid bounce in an inelastic collision. Three modes developped for this one : following Main Structure, running around the planet, and following Gravitron.
Implemented two colors to highlight targets : white is auto while red is manually selected.
Implemented a key to get back to no target selected.
Modified the speed of the asteroids in general, and specially the ones launched right through the planet.
Fixed repulsion cost (was not purchasable as cost was zero)
Fixed unwilled target switching when an asteroid gets closer than the targeted one.
Target still switch when targeted asteroid is destroyed (or obviously when a key is pressed).