small updates to README with feature matrix and other improvements
fix readme links
support for schema compatibility
add a bit more pig detail
Merge pull request #71 from Parquet/update_readme

Update Readme
add negative tests
Merge pull request #72 from Parquet/schema_compatibility

support for schema compatibility
fix schema compat
Merge branch 'master' into schema_compatibility
Merge pull request #75 from Parquet/schema_compatibility

Schema compatibility fix