Add support for modernc.org/sqlite

[cugu]

This PR adds a new dbmate driver for https://modernc.org/sqlite.

Some Go projects like sqlc moved away from github.com/mattn/go-sqlite3 to modernc.org/sqlite which offers sqlite support without cgo.

This PR adds a new dbmate driver for modernc.org/sqlite with the following changes:

• The new package pkg/driver/sqlite/internal contains the common sqlite code for both sqlite drivers. This is mostly just moved over from the previous pkg/driver/sqlite package, not sure why git did not pick this up.
• The new pkg/driver/sqlite/modernc contains a dbmate driver for modernc.org/sqlite. It imports modernc.org/sqlite and registers the appropriate dbmate drivers. Also contains the tests for this dbmate driver.
• The updated pkg/driver/sqlite package still imports github.com/mattn/go-sqlite3 and registers the appropriate dbmate drivers. This is a backwards compatible wrapper of the internal package now and still contains tests for this driver.
• main_non_cgo.go imports the new modernc driver, so dbmate can be build without cgo now and still has sqlite support.

[amacneil]

Thanks for the PR

• Could you explain more about why this matters for your workflow? Most people are using a compiled binary of dbmate so the fact that we use cgo is irrelevant
• What is modernc/sqlite? The website you linked is very light on details and just says "CGo-free port of the C SQLite3 library". What does that mean? Does it mean they ported sqlite to go? Or this is somehow a precompiled sqlite?
• If we did move to "modernc" sqlite, why keep the existing sqlite driver at all? Are they incompatible?

[cugu]

Could you explain more about why this matters for your workflow? Most people are using a compiled binary of dbmate so the fact that we use cgo is irrelevant

I am using dbmate as a library in some projects, here is an open source example if you are interested. I prefer to avoid cgo, to make (cross-) compilation easier. I adapted the dbmate sqlite driver to use modernc.org/sqlite: cugu/fomo/…/dbmate_sqlite.go and wanted to share it here in case others want to use it as well.

What is modernc/sqlite? The website you linked is very light on details and just says "CGo-free port of the C SQLite3 library". What does that mean? Does it mean they ported sqlite to go? Or this is somehow a precompiled sqlite?

modernc.org/sqlite is created by translating the sqlite C code to Go code using https://modernc.org/cc. So the sqlite is native Go code then, but autogenerated and not pleasant to read. It is precompiled in the sense that the C code is compiled to Go, but it does not contain any sqlite binary.

If we did move to "modernc" sqlite, why keep the existing sqlite driver at all? Are they incompatible?

The existing driver, using github.com/mattn/go-sqlite3, might be faster and for other projects that use it anyway it might make sense to not add both sqlite drivers as dependencies.

Also for fully moving to modernc.org/sqlite I felt this would be a more disruptive change here and I tried to not break anything. It would make (cross-) compilation of dbmate easier though as well.