Javadoc correction for ArrayAnimator

Corrected error in Javadoc for interp methods. Val is a value between min and max, not 0.0 and 1.0.

revert change to SpanningTree for now; to discuss: directed spanning trees

Added initialization of spanning tree outside build routine. This allows a extension of SpanningTree to, for instance, a DirectedSpanningTree where only the buildSpanningTree(Node root) method needs to be overridden. As it was, buildSpanningTree contained calls to super.setRoot() and if SpanningTree was overridden, there was no way to set root anymore. Now initialize(Root) can be called. Didn't want to allow access to SpanningTree.setRoot() as that API should not be used for spanning trees.

Changed error reporting to adding columns to tables so that "column already exists" exception is not hidden by AbstractTupleSet.addColumns(Schema). But, the IllegalArgumentException is only generated when one attempts to add a column with an existing name and a different type (re-add column with same name & type has no effect [reverted to the previous behaviour]).

fixed Javadoc on Visualization.addAggregates(String, Schema)

Clarified use of addAggregates(String, Schema) in Javadoc; if Schema doesn't extend VisualItem.SCHEMA then missing column exceptions are generated when visualizing aggregates.

In addColumn methods, removed hiding of IllegalArgumentException thrown when a column with the same name is added twice.

Added rescheduling bug fix

Fixed javadoc comments

Updated license and readme files

Made minor adjustments to ObjectColumn and ExpressionParserTokenManager to remove compiler warnings

Added root node checks to TreeNodeIterator to avoid iteration errors

Added patch to TreeMLWriter to avoid dumping null values (Patch #1758889 from mwlinnem)

Added new readers/writers for fixed width text data table formats