SQLite3 ported to use LMDB instead of its original Btree code.

To set the LMDB mapsize in pages, use:

PRAGMA max_page_count=<integer>;

Using tool/speedtest.tcl in the SQLite source tree, the time to insert 1000 records on my laptop SSD was 22.42 seconds using the original code, and only 1.06 seconds using LMDB. Both tests were run 3 times, with results averaged. The actual runtimes were

Original    MDB
23.14        1.07
22.02        1.05
22.12        1.08

Tested at version 3.7.7.1.

More recent test results using 3.7.17 are on pastebin, summarized below:

	SQLite	SQLightning
Operation times in microseconds, lower is better
Sync Seq Write	8175.371	6171.233
Sync Rand Write	8308.706	6231.249
Seq Write	25.587	31.778
Batch Seq Write	7.402	7.087
Rand Write	33.235	32.902
Batch Rand Write	18.847	13.754
Rand Read	22.645	7.685
Seq Read	7.557	1.551
Rev Seq Read	7.456	1.531