Added .gitignore

No project should be without one! :)
Refactored get accessor for gasLevel

Generally, the convention for creating public getters for private
instance variables is to name them as follows:
```
//…
private double someVar;
public double getSomeVar() {
  return this.someVar;
}
//…
```
"xx gallons of gas left" report now uses getGasLevel() accessor

Since the Car class knows its own gas level, and provides a public get
accessor for it, there isn’t a reason (that I can think of) to locally
compute the gas level.
getGasLevel() now guards against negative numbers
drive() is now a more-accurate simulation

I expanded the drive() method of the Car class to model a couple of
things:
- Maximum distance possible
- Distance the driver intends to drive
- Actual distance driven

Additionally, I added range checking: maximumDistance and
intendedDistance can’t be less than zero; actualDistance can’t be
greater than maximumDistance.

Finally, drive() now returns the actualDistance (actual distance
driven), as a double.
Added output showing number of miles actually driven

Also notice that the (previously named) milesDriven variable has been
refactored to “milesToDrive”, while a new “milesDriven” variable has
been created to hold the actual miles driven.
Updated to account for renamed gasLevel accessor
Removed .class files
Updated comments
Corrected Javadoc parameters for addGas method

Previous param name “gasLeft” didn’t match the method signature of
“public void addGas(double amountGas)”
Regenerated documentation

Reflects changes made on 12/18/2013
Added project-specific readme
Merge pull request #1 from gregkrsak/master

Improvements to the simulation characteristics of "Car Project"