added max_results argument to list_tables()
Merge pull request #36 from Mullefa/master

added max_results argument to list_tables()
Cleanup default handling for list_tables.
Fix CSV quote encoding.

BigQuery expects strings to be quoted in the "usual" manner, meaning that
quotes in string fields should be doubled, with the field itself in quotes.

This accomplishes this by tweaking arguments to `encodeString` and
`write.table`, and (unfortunately) quotes all string fields as a side-effect.