Allow to specify an objectToExportTo for goog.exportSymbol

This allows users to build ol3 without anything exposed in the
global namespace. This can e.g. be useful for creating an ol3
AMD module, by simply using a build configuration with
"define('ol',function(){var o={};%output%return o.ol;});" as
"output_wrapper".
Document the new namespace option
Remove unused goog.require
Merge pull request #2092 from fredj/unused-require

Remove unused goog.require
opt_dest should be assigned to not pushed
Pass around single config object
Additional doc for the namespace option

People should be discouraged from exporting to single letter namespaces to avoid collissions with the symbols generated by the compiler.
Merge pull request #2082 from ahocevar/custom-exports-target

Allow to specify an objectToExportTo for goog.exportSymbol
Test that a custom geometry works
Merge pull request #2095 from ahocevar/test-geometry-name

Test that a custom geometry works
Ability to specify geometryName on ol.format.GeoJSON
Merge pull request #2097 from bartvde/geojson-geometryname

Ability to specify geometryName on ol.format.GeoJSON (r=@tschaub)
Merge pull request #2093 from bjornharrtell/fix_opt_dest2

Assign to provided array instead of pushing when getting a linestring midpoint.
snapshot