fix: cassandra metadata driver blocksize

Cast blocksize to integer.
The reference driver of sqlite has the same implementation.
fix: transport errors while using markers, offset

These errors were brought into the picture, when testing with the
cassandra metadata driver.

- The offsets were being cast to int, but not being explicitly passed down
  to the metadata layer.
- Falcon sets the return of req.get_param() to None automatically, if the
  param is not present.
comments: Add comments about req.get_param

Per Xuan's Suggestions, comments now are added explaining that
falcon would return None, if it cant find a parameter.
Merge pull request #165 from TheSriram/transport_fixes

Cassandra and Transport fixes