New octicon class names

Strip contents of <script> tags.

Include output and results to filter, pipeline event payload

Add an `instrumentation_name` attribute to the Pipeline. Events report
this name for the originating pipeline.

Add `setup_instrumentation` method to the Pipeline. Sets the
instrumentation name and service.

Not necessary because there is no such class to load.

Instrument filters in the pipeline

Add an html-pipeline executable to the gem

Usage: html-pipeline [-h|--help|help] [-f|--filters]
       html-pipeline [FILTER [FILTER [...]]] < file.md
       cat file.md | html-pipeline [FILTER [FILTER [...]]]

Also stop gitignoring bin/, but ignore exec/ instead for binstubs.

add result[:mentioned_usernames] for MentionFilter

Bump escape_utils

Conflicts:
	README.md

Don't monkeypatch Nokogiri in 1.9