No way to check column type by column name

[Justin Nuß]

When writing functions that want to check the type of a column (via (*Stmt).ColumnType) users need to know the index of the column since there is no way to get the index for a column by its name. This is inconvenient and error prone since column indexes depend on the order of columns in a query and can easily be forgotten when changing a query.

Possible solutions:

1. Add a variant of ColumnType that takes a column name
2. Add a method to return the index for a column by its name