Update CHANGELOG.md
Update CHANGELOG.md

Record improvements and bug fixes in ~month since 0.3.0 release.
geopandas/geopandas,ozak/geopandas,geopandas/geopandas,jorisvandenbossche/geopandas,jorisvandenbossche/geopandas,jdmcbr/geopandas,ozak/geopandas,jdmcbr/geopandas,jorisvandenbossche/geopandas,geopandas/geopandas