Add passing tests, refactor to introduce forEachLine.

test/consistent_bullet_styles_asterisk.md

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+* Item
+  * Item
+  * Item

test/consistent_bullet_styles_dash.md

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+- Item
+  - Item
+  - Item

test/consistent_bullet_styles_plus.md

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++ Item
+  + Item
+  + Item

test/fenced_code_blocks.md

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+This is a GFM-style fenced code block:
+
+``` bash
+#!/bin/bash
+
+# Print something to stdout:
+echo "Hello"
+echo "World"
+```
+
+This is a kramdown-style fenced code block:
+
+~~~ bash
+#!/bin/bash
+
+# Print something to stdout:
+echo "Hello"
+echo "World"
+~~~
+
+None of the above should trigger any heading related rules.

test/first_header_good_atx.md

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+# Header

test/first_header_good_setext.md

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+Header
+======

test/header_mutliple_h1_no_toplevel.md

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+Some introductory text
+
+# Heading 1
+
+# Heading 2