Create multiple prepared statments for concurrent access

[mwatts15]

Draft
Errors similar to issue #31 have necessitated the introduction of locking around access to SQLite prepared statements in the FileCabinet component and this sort of locking will be added to TagDB statements as well. This has brought up the question of whether there may be a slow-down in operations due to lock-contention. This proposal attempts to address the question of whether this is a problem that needs attention and then to suggest a solution in the case that it does.

1. Determine if there is significant contention over access to prepared statements. Resolving issue Get automated source coverage information for unit tests #25 would be helpful here.
2. Use statement semaphores to allocate replicates of the prepared statement and make the semaphore tables 2D.