New direction for handling failed flowrecords

[BThacker]

The idea behind this is to simply try catch the init of FlowRecord, and if an exception is caught, increment the "skipped_records" field of the basereader class. This value can then be checked and logged in the consuming class for further investigation if warranted. Also added an override during class init to raise the exception instead.

[bbayles]

Suggestions:

• Catch more than just ValueError - why not any Exception?
• Do self.skipped_records = 0 in the reader class init and increment it when handling an exception

[BThacker]

Added skipped records to the base reader, added all exceptions to the catch (good point)

[BThacker]

Dropped the multiple return types and just incremented the counter instead. Consuming modules can check the skipped record value and then log based on that.

[BThacker]

removed the unnecessary var creation, direct to yield