Properly indent after optional close tag #188

Description

Auto indentation should use knowledge of optional closing tags

Steps to Reproduce

1. Blank document
2. Save as bob.html
3. Type:

<!doctype html>
<html>
<head>
  <title>Yo</title>
  <body>

Expected behavior: [What you expect to happen]

Upon typing the last > in <body> (or, alternatively, typing the space in <body class=...) that <body> line should be indented left. In other words, the same indentation level as the <head> line.

Actual behavior: [What actually happens]

The <body> line is indented as a subordinate (one level deeper of indentation) than the <head> line.

Reproduces how often: [What percentage of the time does it reproduce?]

100%.

Versions

Atom : 1.23.3
Electron: 1.6.15
Chrome : 56.0.2924.87
Node : 7.4.0

macOS 10.13.2 (17C205)

Additional Information

<head> => <body> is only one such scenario included in this issue. For a full list of optional close HTML tags, see O in the "End tag" column of https://www.w3.org/TR/html4/index/elements.html (I can't find the HTML5 version of this document).

See also https://www.w3.org/TR/html51/syntax.html#in-head for more discussion of HTML5 tokenization and tree building.

See also https://www.w3.org/TR/html51/syntax.html#the-stack-of-open-elements for discussion of special HTML5 elements.