feat: add the inline tag and json-style omitempty

Assisted-by: GLM 5.3 Flash

docs/API.md

@@ -475,22 +475,30 @@ nil map emits nothing.
 
 ### Tag options
 
-The part of a `toml` tag after the first comma carries options. Both options
-shape emission only; the decoder ignores them.
+The part of a `toml` tag after the first comma carries options. They shape
+emission only; the decoder ignores them, so a value that round-trips keeps
+its key whether the table it came from was written inline or under a header.
 
 - `omitzero` skips the field when its value is the zero value of its type. A
   type with an `IsZero() bool` method (time.Time among them) decides through
   that method, so a zero `time.Time` or an all-zero struct disappears from
   the output.
-- `omitempty` skips the field when it holds an empty collection: a nil or
-  empty slice or array, or a nil or empty map. Strings and other scalars are
-  not covered by `omitempty`; use `omitzero` for those.
+- `omitempty` skips the field when it holds an empty value in the
+  encoding/json sense: an empty string, a zero number, `false`, a nil pointer
+  or interface, and a nil or empty slice, array or map. This is a change of
+  semantics against 1.x, where only collections were covered.
+- `inline` forces a struct or map field to emit as `name = {…}`, the inline
+  table form, instead of a header section, whatever its size; a named
+  embedded struct tagged this way does the same. A field holding an array of
+  tables is an error under `inline`, because the inline form would re-parse
+  as a value array and change the value's Go type.
 
 ```go
 type Config struct {
 	Host    string    `toml:"host,omitzero"`
 	Started time.Time `toml:"started,omitzero"`
 	Tags    []string  `toml:"tags,omitempty"`
+	Retry   Retry     `toml:"retry,inline"`
 }
 ```