This commit includes the HW2 design document and logistics document.

It also includes the InvalidSQLException to throw when a SQL query has
a semantic error.

NanoDB client now supports shell commands of the form \cmd, which are
handled within the InteractiveClient, not by the server.  There are two
commands:

\help prints out useful help information

\source filename.sql will run all commands contained in the file
filename.sql

There are surely interesting wrinkles to iron out.  For example, if the
sourced file contains an "EXIT" command then it will exit the client.
Also, an error should probably terminate the evaluation of a sourced
file, but currently it does not.

A number of correctness tests are contained in the TestHeapTableFormat
class.  The tests are activated in the Maven test configuration.

The Buffer Manager concurrency test wasn't closing the data files it
created, so they couldn't be deleted during the cleanup phase on
Windows.  This caused test failures on Windows but not on *nix.

Somehow when upgrading the NanoDB parser to ANTLR4, I forgot to include
the SHOW STATS command.  This is essential for the storage lab, so of
course I added it back in as quickly as possible.

Some tests were failing on my box because I've got my locale set to
Portuguese; this shouldn't be an issue, since the NanoDB tests are
explicitly written in English. In order to fix Date parsing language-
agnostically, I just explicitly set the locale to `Locale.ENGLISH`.

The Buffer Manager wasn't tied into the property-registry mechanism,
so it wouldn't notice when the page-cache size was changed.  This is
now hooked together with a property-observer interface.