add symbol tracking to schematic for nodes, connections, constraints
Merge branch 'master' into symboltable

Conflicts:
	src/main/java/org/whdl/intermediate/Schematic.java
Update README.md
Update README.md
Restored coveralls support
refactor MultipleAssignmentException
Merge pull request #102 from mtrberzi/symboltable

Implement symbol table
Merge pull request #103 from manifold-lang/coveralls-69

Restored coveralls support
Create AttributeSet for use by Nodes and Ports #81

Not doing verification against list of possible attribute names and
types yet.
Rename to Attributes, use in more places

Updating Connection and Constraint to use Attributes abstraction.

updating unit tests as well.