Bugsnag handler will process extra fields.

This is nice if you have custom logging set up to add extra attributes
to your logRecord 's .  You can now tell the bugsnag handler what
these fields are and it will add them to tabs for you, safely
checking if they exist first.
Fix logic error in handlers
Param is called meta_data not metadata :/
mimic old behavior of extra_data tab instead of extra
Add description of new feature
remove extra_data and other deprecated meta data
forgot closing )
Merge pull request #48 from HurricaneLabs/allow_extra_record_fields

Allow extra record fields in BugsnagHandler