Fix SQLite add Columns schema
SQLite add Columns schema only allows one column to be added at a time. Schema grammar (and associated) has been altered to return the proper SQLite statements for adding columns. Although there are no test cases that run SQLite as part of the Framework package, I have tested these locally with SQLite, and the corrections work. See: http://www.sqlite.org/lang_altertable.html
Merge pull request #484 from karptonite/sqlite_addcolumns_patch

[Bugfix]Fix SQLite add Columns schema