Driver Tweaks
Merging in new driver code.
Merge branch 'gurupras@buffalo.edu' of https://github.com/okennedy/worldtree into gurupras@buffalo.edu

Conflicts:
	src/Driver.java
Merge branch 'gurupras@buffalo.edu' of github.com:okennedy/worldtree into gurupras@buffalo.edu
Added workaround for a bug introduced by a recent change to Expr class

The removal of baseExpr field from Expr class led to storing all of
baseExpr fields within 'this'. This led to issues especially with
the retrieval of Expr.property (see FIXME in Expr.value())

This commit forces 'this' to take baseExpr.property as its property
in the ARITH constructor case
Working on basic expression handling
Added comments to container classes
Merge branch 'gurupras@buffalo.edu' of github.com:gurupras/worldtree into gurupras@buffalo.edu
Merge branch 'gurupras@buffalo.edu' into working
Added missing interface condition() to IExpr

Updated Expr class' constructors to use baseExpr fields for all
of this' fields wherever applicable
Resolved a FIXME in Expr.value() method by removing the controversial
piece of code
BasicSolver now has code to handle expressions

This is in no way a complete solution and is almost guaranteed to
have bugs. However, it is a decent platform to build up from.
Added sample files for simple dependency in definitions