Stricter typechecking

[trevyn]

SQLite is flexibly typed, a philosophy which doesn't harmonize well with Rust's preference for strong types.

Despite this flexible typing, SQLite provides access to the underlying type of result columns of individual rows, and rusqlite exposes this via, for example:

• rusqlite::Row::columns()
• rusqlite::Column::decl_type()
• rusqlite::Row::get_raw()
• rusqlite::types::ValueRef

These can be used to enforce additional typechecking at runtime, instead of the usual behavior of coercing types.

[trevyn]

Also incoming soon: SQLite STRICT tables:

https://www.sqlite.org/draft/stricttables.html

Doesn't directly support BOOLEAN, but other than that pretty nice. Note that derived columns should still be runtime typechecked!