PARQUET-292: Update CHANGES.md for 1.8.0.
PARQUET-292: Update CHANGES.md for 1.8.0.

Also, cleaning up PRs: closes #206, closes #47, closes #72, closes #87,
closes #96, closes #100, closes #107, and closes #112.

rdblue/parquet-mr,winningsix/incubator-parquet-mr,rdblue/parquet-mr,winningsix/incubator-parquet-mr,jaltekruse/parquet-mr-1,laurentgo/parquet-mr,HyukjinKwon/parquet-mr,DataDog/parquet-mr,SinghAsDev/parquet-mr,nitin2goyal/parquet-mr-1,cchang738/parquet-mr,HyukjinKwon/parquet-mr-1,SinghAsDev/parquet-mr,coughman/incubator-parquet-mr,Zariel/parquet-mr,Zariel/parquet-mr,coughman/incubator-parquet-mr,nezihyigitbasi-nflx/parquet-mr,winningsix/incubator-parquet-mr,HyukjinKwon/parquet-mr-1,saucam/incubator-parquet-mr,DataDog/parquet-mr,sworisbreathing/parquet-mr,nguyenvanthan/parquet-mr,nitin2goyal/parquet-mr-1,laurentgo/parquet-mr,saucam/incubator-parquet-mr,HyukjinKwon/parquet-mr,sworisbreathing/parquet-mr,DataDog/parquet-mr,nguyenvanthan/parquet-mr,sircodesalotOfTheRound/parquet-mr,zhenxiao/parquet-mr,cchang738/parquet-mr,nguyenvanthan/parquet-mr,nitin2goyal/parquet-mr-1,saucam/incubator-parquet-mr,zhenxiao/parquet-mr,jaltekruse/parquet-mr-1,HyukjinKwon/parquet-mr-1,jaltekruse/parquet-mr-1,apache/parquet-mr,laurentgo/parquet-mr,sworisbreathing/parquet-mr,piyushnarang/parquet-mr,rdblue/parquet-mr,piyushnarang/parquet-mr,SaintBacchus/parquet-mr,coughman/incubator-parquet-mr,sircodesalotOfTheRound/parquet-mr,HyukjinKwon/parquet-mr,sircodesalotOfTheRound/parquet-mr,apache/parquet-mr,nezihyigitbasi-nflx/parquet-mr,zhenxiao/parquet-mr,piyushnarang/parquet-mr,cchang738/parquet-mr,SinghAsDev/parquet-mr,SaintBacchus/parquet-mr,Zariel/parquet-mr,apache/parquet-mr,SaintBacchus/parquet-mr,nezihyigitbasi-nflx/parquet-mr