Replaced string arg with io.Reader in Block().

Requested fix for Issue #2.
Block() function definition needed to be changed since getting the
filesize was no longer the responsibility of Block() but of the caller.

If there is a better way without doing it would be nice.
Changed to more descriptive argument
Removed .test files and added to ignore.
Use the testing Fatal method instead of log.
Refactored as per @jsimnz recommendations.
Merge pull request #5 from dkua/block

Replaced string arg with io.Reader in Block().