Add examples/lerax-square-platform.cpp

[ryukinix]

CHANGELOG:

• w/s keys now increase/decrease the square
• simple gravity effect implemented
• jump scheme implemented
• if you press left shift the player will double the x-velocity when still pressed
• add blocks to act as platform
• add collision detection system for blocks

TODO

• [x] this should a separated example instead of overwriting examples/lerax-square.cpp
• [x] debug should be called on update or render

[ryukinix]

Please, squash before merge!

[ryukinix]

I'll merge that as it is, other improvements should be done on #11 or in another PR.