Add Windows support.
add Cursor.Delete()
Add Windows support.

This commit adds Windows support to Bolt. Windows memory maps return an address instead of a byte
slice so the DB.data field had to be refactored to be a pointer to a large byte array.
Remove errcheck.
Merge pull request #190 from Shopify/cursor_delete

Add Cursor.Delete()
Merge pull request #191 from benbjohnson/win-ftw

Windows Support