Ch4, Ex.1: Explicitly name the scale argument in stats.expon()

In scipy 0.12.0, the first unnamed argument becomes the location of the distribution. As such, the starter code gives the reader an Exp(1) distribution starting at x=4.
Merge pull request #73 from mbauman/patch-1

Ch4, Ex.1: Explicitly name the scale argument in stats.expon()
Minor changes to README.md's grammar

I've corrected a few comma errors and properly formatted some nouns (e.g., correcting "Scipy" to "SciPy" or italicizing a television show name), thus making the text impervious to assaults from future grammarians.
Merge pull request #74 from ajduberstein/master

A first-round of proofreading