Teach ThreadBuffer to read from a URL
Remove unnecessary imports

These objects are in the same package as the Test, and thus do not require import.
Teach Reader to load from a URL

Updated the test to exercise both the File and the URL flavors.
Attach the sources during packaging

Since this project is Open Source, it is very handy to have Maven
download the sources for the jars found in central.

Some projects also attach javadoc, but the sources provide javadoc
(at least with IJ) so I find that they just take up space.
Refactor to InputStream instead of URL

InputStream is the common denominator and contains enough information to
construct the ThreadBuffer (and thus the Reader).
Remove unnecessary throws declarations

Those warnings in IJ hide potentially real bugs.
Merge branch 'read-from-url' of github.com:mdaniel/MaxMind-DB-Reader-java into greg/input-stream
Formatting. Changed static factory method to constructor.