Add experimental support for watchOS

This patch was authored by @hyouuu and released by @0xTim.

Adds watchOS adds a target platform to enable it to be built for that platform.

Note: watchOS support is very much experimental and not currently a supported platform, though there is no reason why it shouldn't work

Drop support for Swift 5.4

This patch was authored and released by @gwynne.

Minimum supported version is now Swift 5.5.

Also includes the same upgrades to CI as those found in vapor/sqlite-kit#100 (most notably, adding the API breakage check and code coverage).

Explicitly handle a custom ID key set to the empty string

This patch was authored and released by @gwynne.

Treat it as meaning not to retrieve an inserted ID value. This is in support of upcoming FluentKit feature work.

Add configurable connection pool timeout

This patch was authored by @madsodgaard and released by @0xTim.

Adds option to configure the connection pool timeout (#74)

databases.use(.sqlite(.memory, connectionPoolTimeout: .minutes(1)), as: .sqlite)

Minimum iOS version is 13

This patch was authored and released by @calebkleveter.

The minimum iOS version supported by this package is now iOS 13 since the SqliteKit dependency requires it.

FluentSQLiteDriver 4.0.0

This patch was authored and released by @tanner0101.

Docs:
https://docs.vapor.codes/4.0/fluent/overview/
https://docs.vapor.codes/4.0/fluent/model/
https://docs.vapor.codes/4.0/fluent/relations/
https://docs.vapor.codes/4.0/fluent/migration/
https://docs.vapor.codes/4.0/fluent/query/
https://docs.vapor.codes/4.0/fluent/schema/
https://docs.vapor.codes/4.0/fluent/advanced/

More information on Vapor 4 official release:
https://forums.swift.org/t/vapor-4-official-release-begins/34802

Clarify ALTER TABLE restrictions

This patch was authored and released by @tanner0101.

Adds new checks and error messages to clarify SQLite's ALTER TABLE restrictions (#66, fixes #62).

FluentKit 1.0.0 GM

This patch was authored and released by @tanner0101.

Updates this package for compatibility with latest version of FluentKit.

Removed '.' from FluentKit Dependency Version Identifier

This patch was authored and released by @calebkleveter.

Fix SQLiteError's DatabaseError conformance

This patch was authored and released by @tanner0101.

SQLiteError now correctly conforms to DatabaseError (#50, fixes #49).