POM-9. Upgrade to Avro 1.7.5

issue: https://jira.kiji.org/browse/POM-9
review: https://review.kiji.org/r/1015
SCORE-79. MutliBufferedWriter should expose a SingleBuffer view which does not require the user to keep track of a buffer name.

issue: https://jira.kiji.org/browse/SCORE-79
review: https://review.kiji.org/r/992
SCORE-75. SCORE-75. Reimplements FreshKijiTableReader with improved concurrency

issue: https://jira.kiji.org/browse/SCORE-75
review: https://review.kiji.org/r/1017