bugfix: reorder fields in thrift struct caused writting nulls. fixed it by keeping track of which fields are being written in each level, and only write nulls when current level is finished in MessageColumnIO
rename var
remove fieldCount from marker
format
Merge pull request #298 from Parquet/bugfix_reorder_thrift_fields_causing_writting_nulls

Bugfix reorder thrift fields causing writting nulls