docs: Fix some broken links (#2913)

Author: andrewmbenton

docs/howto/managed-databases.md

@@ -13,7 +13,7 @@ built-in query analysis engine. PostgreSQL support is available today, with
 MySQL on the way.
 
 Once configured, `sqlc` will also use managed databases when linting queries
-with [`sqlc vet`](vet.html) in cases where your lint rules require a connection
+with [`sqlc vet`](vet.md) in cases where your lint rules require a connection
 to a running database.
 
 Managed databases are under active development, and we're interested in
@@ -78,9 +78,9 @@ sql:
 
 With managed databases configured, `sqlc vet` will automatically create a hosted ephemeral database with your
 schema and use that database when running lint rules that require a
-database connection, e.g. any [rule relying on `EXPLAIN ...` output](vet.html#rules-using-explain-output).
+database connection, e.g. any [rule relying on `EXPLAIN ...` output](vet.md#rules-using-explain-output).
 
-If you don't yet have any vet rules, the [built-in sqlc/db-prepare rule](vet.html#sqlc-db-prepare)
+If you don't yet have any vet rules, the [built-in sqlc/db-prepare rule](vet.md#sqlc-db-prepare)
 is a good place to start. It prepares each of your queries against the database
 to ensure the query is valid. Here's a minimal working configuration:
 
@@ -128,4 +128,4 @@ sql:
   engine: postgresql
   database:
     managed: true
-```
+```

docs/reference/changelog.md

@@ -382,7 +382,7 @@ rules:
     !(postgresql.explain.plan.plans.all(p, has(p.index_name) || p.plans.all(p, has(p.index_name))))
 ```
 
-The expression environment has two variables containing `EXPLAIN ...` output, `postgresql.explain` and `mysql.explain`. `sqlc` only populates the variable associated with your configured database engine, and only when you have a [database connection configured](../reference/config.html#database).
+The expression environment has two variables containing `EXPLAIN ...` output, `postgresql.explain` and `mysql.explain`. `sqlc` only populates the variable associated with your configured database engine, and only when you have a [database connection configured](../reference/config.md#database).
 
 For the `postgresql` engine, `sqlc` runs
 

docs/reference/datatypes.md

@@ -4,7 +4,7 @@
 database types to Go types. Choices for more complex types are described below.
 
 If you're unsatisfied with the default, you can override any type using the
-[overrides list](./config.html#type-overriding) in your `sqlc` config file.
+[overrides list](config.md#type-overriding) in your `sqlc` config file.
 
 ## Arrays
 
@@ -246,4 +246,4 @@ SELECT * FROM shapes;
   	}
   ]
 }
-```
+```

docs/reference/macros.md

@@ -116,4 +116,4 @@ Since the `/*SLICE:ages*/` placeholder is dynamically replaced on a per-query
 basis, this macro can't be used with prepared statements.
 
 See a full example in [Passing a slice as a parameter to a
-query](../howto/select.html#mysql-and-sqlite).
+query](../howto/select.md#mysql-and-sqlite).