format
deprecate and remove group_var_int encoding
Merge pull request #73 from Parquet/reformat_delta

reformat encodings
add mention of boolean on RLE
Merge pull request #76 from Parquet/boolean_rle_encoding

add mention of boolean on RLE
Merge pull request #74 from Parquet/remove_group_var_int

deprecate and remove group_var_int encoding
Merge branch 'master' into new_data_page_type
address review comments: default value and unused field