Levels and better playability

In the latest version of Altay, I've tried to improve the user experience by implementing Levels.

The player passes Levels, depending on the experience they gain in the game. This is established basically by increasing the Level as the score passes certain milestones.

As Levels increase, enemies start to show up faster and faster. And, beyond Level 10 it's almost impossible to play the game.

In this current version, some players reported that the game is too difficult for a beginner, starting from Level:1. 

The movement of the Tank is dynamic, and players have reported that they like how the Tank moves (floats with acceleration). Let me know, if you like it or not.

Powerups are a bit more balanced in this version too.

Besides these, the following ideas are worth mentioning:

• Init Game memory (kill and reinit)

• add sounds

• info popup for powerups (similar to CrimsonLand?)

• add a super bomb powerup

• add timeout for powerups in inventory

Let me know what you think about the game! And you can always comment on the game, asking for a question or making a request for a feature to add.