Allow ALTER TABLE to operate on columns without COLUMN keyword

[brandonpayton]

This PR adds support for the following valid ALTER TABLE syntax:

ALTER TABLE <table-name> ADD <column-name> <data-type>;

and

ALTER TABLE <table-name> DROP <column-name>;

Prior to this PR, these queries do not work and result in error conditions.

For reference, here is the documented SQLite syntax for ALTER TABLE queries:
https://www.sqlite.org/syntax/alter-table-stmt.html

It shows that the COLUMN keyword is optional, and I've successfully tested syntax without the COLUMN keyword in both MySQL and SQLite.

Reported by @JanJakes