Added support for checking for a file content result.

Partial implementation of #3.
Added support for checking a file content result's binary contents.

Partial implementation of #3
Added support for checking a file content result's content type.

Partial implementation of #3.
Deprecated ShouldRenderFile.

Partial implementation of #3.
Tweaked file contents error message formatting.
Refactored certain file methods to test the content type first.

Partial implementation of #3
Merge pull request #23 from ByteBlast/master

Implemented ShouldRenderFileContents and deprecated ShouldRenderFile