gfm tests:

```

% pandoc -f gfm -t native

| Fruit | Price |

| ----- | ----: |

| apple | 0.13  |

| orange|1.12|

^D

[Table [] [AlignDefault,AlignRight] [0.0,0.0]

 [[Plain [Str "Fruit"]]

 ,[Plain [Str "Price"]]]

 [[[Plain [Str "apple"]]

  ,[Plain [Str "0.13"]]]

 ,[[Plain [Str "orange"]]

  ,[Plain [Str "1.12"]]]]]

```

```

% pandoc -f gfm -t native

~~stricken out~~

^D

[Para [Strikeout [Str "stricken",Space,Str "out"]]]

```

```

% pandoc -f gfm -t native

# Header

## Header

# -foo-bar_baz

^D

[Header 1 ("header",[],[]) [Str "Header"]

,Header 2 ("header-1",[],[]) [Str "Header"]

,Header 1 ("-foo-bar_baz",[],[]) [Str "-foo-bar_baz"]]

```

```

% pandoc -f gfm -t native

My:thumbsup:emoji:heart:

^D

[Para [Str "My\128077emoji\10084\65039"]]

```

```

% pandoc -f gfm -t native

"hi"

^D

[Para [Str "\"hi\""]]

```

```

% pandoc -f gfm+smart -t native

"hi"

^D

[Para [Str "\8220hi\8221"]]

```

```

% pandoc -t gfm -f native

[Table [Str "The",Space,Str "caption."] [AlignDefault,AlignRight] [0.0,0.0]

 [[Plain [Str "Fruit"]]

 ,[Plain [Str "Price"]]]

 [[[Plain [Str "apple"]]

  ,[Plain [Str "0.13"]]]

 ,[[Plain [Str "orange"]]

  ,[Plain [Str "1.12"]]]]]

^D

| Fruit  | Price |

| ------ | ----: |

| apple  |  0.13 |

| orange |  1.12 |

The caption.

```

```

% pandoc -f gfm-smart -t gfm+smart

“hi”

^D

"hi"

```

```

% pandoc -f gfm+smart -t gfm-smart

"hi"

^D

“hi”

```

```

% pandoc -f gfm+smart -t gfm+smart

"hi"

^D

"hi"

```

```

% pandoc -f gfm+hard_line_breaks -t native

hi

hi

^D

[Para [Str "hi",LineBreak,Str "hi"]]

```