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PARQUET-859: Flatten parquet/file directory, consolidate file reader, file writer code

I believe this makes the codebase simpler and easier to navigate. By consolidating the file reader/writer code, further refactoring and internal improvements will be less obtuse

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #424 from wesm/PARQUET-859 and squashes the following commits:

c98e3d4 [Wes McKinney] Do not generate Thrift files in source directory
e987f47 [Wes McKinney] Remove superfluous PARQUET_EXPORT
0fb83a8 [Wes McKinney] Consolidate file_reader.h, file_reader-internal.h
ac6e2c5 [Wes McKinney] First cut flattening of parquet/file directory and consolidate writer, writer-internal headers

Change-Id: Ib8502bfc6770f20ad54d412ba2fbf8ebdbe135d5