feat: writes, procedures, Fastify and Express adapters, documentation

docs/dialects.md

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+# Dialects
+
+A dialect is the package that knows one database: how to read its catalog, how to write its SQL, how to run a transaction and what its errors mean.
+
+| Package | Database | Embeds | Writes return rows | Estimated count | Row security |
+|---|---|---|---|---|---|
+| `@crudy/restloom-postgres` | PostgreSQL 13+ | `json_build_object`, `json_agg` | `RETURNING` | planner estimate | yes |
+
+## Postgres
+
+```ts
+import { postgres } from '@crudy/restloom-postgres';
+
+const db = postgres(pool);
+```
+
+- **Transactions:** every request is one transaction, `READ ONLY` for reads, with `SET LOCAL statement_timeout` from `limits.timeoutMs`.
+- **Types:** enums read as text. A domain reads as its base type.
+- **Timestamps:** they are written in the session's time zone, as Postgres writes them in JSON.
+- **Procedures:** calls use named arguments, so the order in the body does not matter.
+
+## Changing how SQL is written
+
+Every piece of SQL comes from one overridable method of the dialect's renderer. To change one, subclass it and pass it in:
+
+```ts
+import { PostgresRenderer, postgres } from '@crudy/restloom-postgres';
+
+class Renderer extends PostgresRenderer {
+    like(expr: string, pattern: string, insensitive: boolean) {
+        return insensitive ? `unaccent(${expr}) ILIKE unaccent(${pattern})` : super.like(expr, pattern, false);
+    }
+}
+
+const db = postgres(pool, { renderer: new Renderer() });
+```
+
+The pieces are listed in [writing a dialect](./writing-a-dialect.md).