Added AbsoluteSourceFilter for changing relative src to Fully Qualified

This is useful if an image is root relative but should really be going through
a cdn, or if the content for the page assumes the host is known i.e. scraped
webpages and some RSS feeds.
Made AbsoluteSourceFilterTest exceptions include their filter class name.

This should help identify what contexts are required for the filter.
Test have also been updated to make sure exceptions are raised when
required contexts are missing and that the exception message includes
the name of the class where the required context is missing.
Raise the roof---I mean, error
Merge pull request #37 from gjtorikian/raise-errors

Raise the roof---I mean, error
bump to 0.0.8
Don't monkeypatch Nokogiri in 1.9
Merge pull request #40 from jch/no-nokogiri-monkeypatch-in-19

Don't monkeypatch Nokogiri in 1.9
Merge remote-tracking branch 'benubois/relative'

Conflicts:
	README.md
Merge branch 'master' of https://github.com/jch/html-pipeline
bump escape_utils and linguist since it uses it too
Merge pull request #41 from brianmario/bump-escape-utils

Bump escape_utils
release 0.0.9
add result[:mentioned_usernames] for MentionFilter
Merge pull request #42 from fahchen/master

add result[:mentioned_usernames] for MentionFilter
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.
Merge pull request #44 from indirect/master

Add an html-pipeline executable to the gem
release 0.0.10
Instrument filtering, test
Doc, clean up instrumentation code
Add default pipeline instrumentation service