Release notes for 0.38.
Release notes for 0.38.

This adds the release notes for 0.38.

seibert/numba,stonebig/numba,seibert/numba,sklam/numba,seibert/numba,stuartarchibald/numba,stonebig/numba,jriehl/numba,sklam/numba,IntelLabs/numba,cpcloud/numba,gmarkall/numba,gmarkall/numba,seibert/numba,cpcloud/numba,jriehl/numba,IntelLabs/numba,stuartarchibald/numba,stuartarchibald/numba,cpcloud/numba,numba/numba,numba/numba,jriehl/numba,gmarkall/numba,numba/numba,stonebig/numba,cpcloud/numba,seibert/numba,IntelLabs/numba,numba/numba,jriehl/numba,sklam/numba,gmarkall/numba,IntelLabs/numba,sklam/numba,cpcloud/numba,gmarkall/numba,IntelLabs/numba,stonebig/numba,jriehl/numba,stuartarchibald/numba,sklam/numba,stonebig/numba,stuartarchibald/numba,numba/numba