Merge pull request #1 from xcurator/devel/refactor

Update
Fixed attribute caching bugs in BasicSchemaExtraction.
(See bottom of mergeWithSchema() function).

In addition, some variable names and function signatures
are changed to be more intuitive.
Revert changes in Attribute.
Merge pull request #8 from yaoeric/devel/refactor

Fixed attribute caching bugs in BasicSchemaExtraction.