Added extra error properties saving

Added `stack` to skipped keys
Removed unwanted assertions against node internals
Merge remote-tracking branch 'origin/master' into dev/arbitrary.error.data
Updated tests to match saving under error key
Moved to saving extra error properties via error type
Added assertions for `extra.errorProperties`
Starting on test for additional `parseError` information
Added extra error properties saving
Reverting back to original library
Attempting other configurations but realizing Sentry wasn't built for this
Copy over arbitrary information from error
Merge pull request #72 from uber/dev/arbitrary.error.data.sqwished

Added extra error properties saving