support more heavily optimised build

[Smattr]

CMake CMAKE_BUILD_TYPE=Release only gives you -O2. Clink as of 38e9285ee13cc854a4b74650777061cc5f3c0bc5 seems to get a significant benefit from LTO. We can likely also get a further speed up from a SQLite amalgamation build. Not of much relevance during development, but for deployment this would be nice.

[Smattr]

Surprisingly an intermediate point in some database normalisation work (5e1c86b655c860512f8a37a180800c34fcb80069) is already showing a 77% speed up in database construction. If we continue on this trajectory, going to an amalgamation build may be unnecessary.