Add Eclipse '.metadata' directory to ignore list

Eclipse's `.metadata` directory is located below the workspace. It contains the `.plugin` subdirectory, which has a lot of code in it - both plugin code and file history from the workspace.

For example, when I `pss`-ed for `connectURI` in my workspace, I got one correct result and a few dozen results from the history in `.metadata`:

    ./.metadata/.plugins/org.eclipse.core.resources/.history/bc/70d26d74bbfe00121178f4cf4000aacf
    23:	private static final String connectURI 	= 	"...jdbcCompliantTruncation=false";
    48:				connection = DriverManager.getConnection(connectURI, username, password);
    53:						connectURI, username, password, e.getMessage());

    ./.metadata/.plugins/org.eclipse.core.resources/.history/c1/80554931e62f0013154c9564f9925bf1
    23:	private static final String connectURI 	= 	"jdbc:mysql://127.0.0.1:3306/pixels?    jdbcCompliantTruncation=false";
    48:				connection = DriverManager.getConnection(connectURI, username, password);
    50:						connection.toString(), connectURI, username));
    54:						connectURI, username, password, e.getMessage());

    ...

I assume that most users would like to view the code in their workspace, rather than Eclipse's plugin and history folders.