SeparatedValueReader dies when columns don't match

otherwise when you are looping through a file using next,
it will just truncate the file and print an error message,
without any other clue that something is wrong.
Merge pull request #279 from apregier/make_svr_die

SeparatedValueReader dies when columns don't match
adding additional documentation
whitespace for readability
Merge pull request #298 from chrisamiller/master

adding additional documentation