Fix freelist allocation direction.

This commit fixes the freelist so that it frees from the beginning of the data file
instead of the end. It also adds a fast path for pages which can be allocated from
the first free pages and it includes read transaction stats.
Fix freelist allocate().
Added new projects.
README
move Copy and CopyFile from DB to Tx
add tx.Size() and ensure tx.Copy() copies exactly that many bytes
review comments
Merge pull request #171 from Shopify/tx_copy

Move Copy/CopyFile from DB to Tx and make sure it copies exactly Tx.Size() bytes
Merge pull request #169 from benbjohnson/allocation

Fix freelist allocation direction.