Bump golangci-lint and (max) Go versions (#219)

Lint is failing with some inscrutable panic (on a commit with no code
changes). Let's try bumping the version in case they fixed it.

Additionally, the new version's github action uses Go 1.19, which means
it pulls in gofmt updates to match the new [doc-comment formatting rules][1].
So I added Go 1.19 to our list of versions to test (fixes #216)
and updated some of our doc-comments to format better in the
new world (mostly using the new link syntax).

[1]: https://go.dev/doc/comment

Test plan: make lint

generate/generate.go

@@ -313,9 +313,9 @@ func (g *generator) addOperation(op *ast.OperationDefinition) error {
 // Generate is the main programmatic entrypoint to genqlient, and generates and
 // returns Go source code based on the given configuration.
 //
-// See Config for more on creating a configuration.  The return value is a map
-// from filename to the generated file-content (e.g. Go source).  Callers who
-// don't want to manage reading and writing the files should call Main.
+// See [Config] for more on creating a configuration.  The return value is a
+// map from filename to the generated file-content (e.g. Go source).  Callers
+// who don't want to manage reading and writing the files should call [Main].
 func Generate(config *Config) (map[string][]byte, error) {
 	// Step 1: Read in the schema and operations from the files defined by the
 	// config (and validate the operations against the schema).  This is all