ARROW-1530: [C++] Install arrow/util/parallel.h
ARROW-1530: [C++] Install arrow/util/parallel.h

We can use this in parquet-cpp or other places where a thread pool executor would be useful

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

Closes #1093 from wesm/install-util-parallel and squashes the following commits:

1d7aeaf7 [Wes McKinney] Install arrow/util/parallel.h

NonVolatileComputing/arrow,wesm/arrow,wagavulin/arrow,laurentgo/arrow,NonVolatileComputing/arrow,kou/arrow,icexelloss/arrow,pcmoritz/arrow,yufeldman/arrow,apache/arrow,siddharthteotia/arrow,kou/arrow,apache/arrow,pcmoritz/arrow,majetideepak/arrow,wagavulin/arrow,NonVolatileComputing/arrow,yufeldman/arrow,renesugar/arrow,xhochy/arrow,laurentgo/arrow,pcmoritz/arrow,wagavulin/arrow,dremio/arrow,laurentgo/arrow,renesugar/arrow,wesm/arrow,itaiin/arrow,apache/arrow,xhochy/arrow,majetideepak/arrow,tebeka/arrow,wagavulin/arrow,icexelloss/arrow,majetideepak/arrow,majetideepak/arrow,yufeldman/arrow,pcmoritz/arrow,itaiin/arrow,NonVolatileComputing/arrow,wesm/arrow,NonVolatileComputing/arrow,cpcloud/arrow,NonVolatileComputing/arrow,yufeldman/arrow,icexelloss/arrow,yufeldman/arrow,NonVolatileComputing/arrow,wesm/arrow,kou/arrow,pcmoritz/arrow,majetideepak/arrow,majetideepak/arrow,cpcloud/arrow,tebeka/arrow,icexelloss/arrow,itaiin/arrow,wagavulin/arrow,pcmoritz/arrow,xhochy/arrow,dremio/arrow,majetideepak/arrow,icexelloss/arrow,NonVolatileComputing/arrow,renesugar/arrow,siddharthteotia/arrow,yufeldman/arrow,majetideepak/arrow,majetideepak/arrow,itaiin/arrow,cpcloud/arrow,dremio/arrow,cpcloud/arrow,itaiin/arrow,itaiin/arrow,NonVolatileComputing/arrow,xhochy/arrow,laurentgo/arrow,wesm/arrow,renesugar/arrow,xhochy/arrow,siddharthteotia/arrow,icexelloss/arrow,wagavulin/arrow,itaiin/arrow,dremio/arrow,laurentgo/arrow,itaiin/arrow,laurentgo/arrow,majetideepak/arrow,pcmoritz/arrow,xhochy/arrow,kou/arrow,icexelloss/arrow,laurentgo/arrow,kou/arrow,cpcloud/arrow,renesugar/arrow,cpcloud/arrow,wagavulin/arrow,xhochy/arrow,wesm/arrow,dremio/arrow,kou/arrow,wesm/arrow,itaiin/arrow,apache/arrow,siddharthteotia/arrow,laurentgo/arrow,apache/arrow,wesm/arrow,pcmoritz/arrow,laurentgo/arrow,wesm/arrow,majetideepak/arrow,wagavulin/arrow,majetideepak/arrow,tebeka/arrow,wagavulin/arrow,wesm/arrow,xhochy/arrow,apache/arrow,majetideepak/arrow,apache/arrow,wesm/arrow,pcmoritz/arrow,icexelloss/arrow,NonVolatileComputing/arrow,cpcloud/arrow,tebeka/arrow,xhochy/arrow,laurentgo/arrow,wagavulin/arrow,renesugar/arrow,dremio/arrow,wesm/arrow,cpcloud/arrow,apache/arrow,itaiin/arrow,wesm/arrow,renesugar/arrow,cpcloud/arrow,apache/arrow,xhochy/arrow,dremio/arrow,siddharthteotia/arrow,itaiin/arrow,siddharthteotia/arrow,yufeldman/arrow,siddharthteotia/arrow,majetideepak/arrow,apache/arrow,laurentgo/arrow,NonVolatileComputing/arrow,yufeldman/arrow,pcmoritz/arrow,tebeka/arrow,icexelloss/arrow,icexelloss/arrow,itaiin/arrow,apache/arrow,cpcloud/arrow,laurentgo/arrow,dremio/arrow,icexelloss/arrow,wesm/arrow,itaiin/arrow,laurentgo/arrow,xhochy/arrow,tebeka/arrow,wagavulin/arrow,kou/arrow,xhochy/arrow,siddharthteotia/arrow,cpcloud/arrow,pcmoritz/arrow,pcmoritz/arrow,apache/arrow,tebeka/arrow,laurentgo/arrow,icexelloss/arrow,xhochy/arrow,kou/arrow,dremio/arrow,tebeka/arrow,cpcloud/arrow,renesugar/arrow,yufeldman/arrow,xhochy/arrow,cpcloud/arrow,dremio/arrow,tebeka/arrow,icexelloss/arrow,renesugar/arrow,kou/arrow,dremio/arrow,kou/arrow,siddharthteotia/arrow,renesugar/arrow,cpcloud/arrow,yufeldman/arrow,siddharthteotia/arrow,pcmoritz/arrow,apache/arrow,pcmoritz/arrow,siddharthteotia/arrow,pcmoritz/arrow,kou/arrow,renesugar/arrow,kou/arrow,tebeka/arrow,wagavulin/arrow,itaiin/arrow,renesugar/arrow,xhochy/arrow,renesugar/arrow,apache/arrow,renesugar/arrow,laurentgo/arrow,kou/arrow,icexelloss/arrow,majetideepak/arrow,renesugar/arrow,kou/arrow,itaiin/arrow,yufeldman/arrow