Exception data is merged with context data
build a consistent merged hash for exception reporters

use Context.log() to log multiple times without re-merging the context
data.
copy, don't mutate the data.

if the maps are being passed through channels, we have to treat them as
immutable.
unnecessary Data{} initialization
Merge pull request #5 from alindeman/exception_data_merges_context

Exception data is merged with context data