Support additional column metadata

[rogerbinns]

SQLITE_ENABLE_COLUMN_METADATA is off by default. When it is on then additional column information is available. Examining the SQLite code shows that the cost of turning on SQLITE_ENABLE_COLUMN_METADATA is 3 additional strdup operations per column in each cursor, which seems rather cheap.

For an externally provided sqlite3 library (ie non amalgamation) the setting is likely off. However we can enable it by default for the amalgamation. There would also be a setup.py --enable flag for external library.

A Cursor.description_fuill() method can then return all the information.