tentative sumOption for EventuallySemiGroup
EventuallyMonoid sumOption tests
rename type parameters and update doc to improve readability
add batching to avoid materializing input in memory
fix batching; add tests
cleanup
address review comments
address review comments
make conditionallyConvert protected
make left protected
fix parameter
Merge pull request #306 from julienledem/eventually_sumOption

add sumOption to EventuallySemiGroup