Issue #151 - add new public methods for enabling logging

Also add public methods which allow avoidance of string builder hit.
Issue #151 - make a pass through code to set appropriate logging tags.
Issue #151 - make a pass through code to pass formatString and var args
Issue #151 - found error when running unit tests
Issue #151 - review changes and fix obvious mistakes
Issue #151 - comment regarding efficiency
Issue #151 - forgot to set default level for TAG_BLOB_STORE
Merge pull request #165 from couchbase/feature/issue_151

Feature/issue 151