Added automatic dependency tree generation to makefile
Added ycm_extra_conf and method to get flags from makefile to it.
Forgot to add flag for system's includes in ycm conf
Added gitignore
Working on base class for game pieces and player control.

Added Ball class which has basic routines for accelerating and moving a
ball. Added PlayerInput struct as an abstract representation of what the
player's "controller" is at a given moment in time. Added and event
handling code for setting the player's desired movement.

Currently, running will generate window and run a simple "game" where
the player (a square) can be accelerated with the arrow keys to a max
velocity.
Added headers that I forgot to include.

Was compiling before due to happy accident in the layout of the
including file.
File comment.
Changed to using vectors to denote direction of movement.
Minor non-functional style changes.
Implemented friction decceleration
Trying to move acceleration rate out of a constant.
Removed trailing semicolon to silence warning.
Moved constant around
Makefile overhaul.
Refactored player input stuff into seperate file from main.
CXX wasn't getting set in makefile properly.
Removed some dead code.
box.pos_ now represents the center of the box.
'q' key now quits the game (for testing purposes).
restructure: DPad::ConsumeSdlKeyEvent -> PlayerInput::ProcessSdlKeyEvent