Exception handling

[ehanson8]

@ghukill comment in PR #175

1. Does this have implications for DeletedRecordEvent? Do we want to update patterns so it has similar default, predictable behavior?
2. Do we want more granular exception classes like InvalidRecordError that extend SkippedRecordEvent, such that we could raise those more meaningful, granular exceptions from code, but still have a single except SkippedRecordEvent: ... logic at the higher level to group skipping behavior for all those child Exception types?

[ehanson8]

Add logging from exception to Transformer.__next__ method

[ghukill]

Also noting that if a field method wants to skip a record, but these more granular exceptions don't feel right, there is nothing wrong with directly raising a SkippedRecordEvent with a meaningful message.