Add support for enabling extended result codes as default on a connection

[intolerable]

• Added support for the SQLITE_OPEN_EXRESCODE sqlite3_open_v2 flag, which enables by-default extended result codes on connections it opens (and also causes sqlite3_open_v2 itself to return extended result codes)
• Added the sqlite3_extended_result_codes function to switch between primary and extended result codes on an existing connection

There's one thing that may need to be changed before this can be merged: with extended result codes enabled for a given connection, there are now two possible "success" results (not counting SQLITE_ROW and SQLITE_DONE) -- SQLITE_OK and SQLITE_OK_LOAD_PERMANENTLY -- while Database.SQLite3.Direct.toResult(M) considers anything not exactly SQLITE_OK to be an error. This shouldn't be a problem unless this library adds support for sqlite3_load_extension, though (https://www.sqlite.org/rescode.html#ok_load_permanently), and should be a simple fix (toResult can mask off the 8 least significant bits before comparing to 0).

[intolerable]

I've added an explicit check for the error, and squashed the branch. do you think anything should be done at this point to handle the OK_LOAD_PERMANENTLY case in toResult? if not, this branch should be mergeable -- thank you for your feedback!

[jchia]

The commit message is way too long. I'm going to change the commit message, commit and push.