test against 2.0
Merge branch 'master' into smart_text
use https in gemfile
register embedded engine for asciidoc

- asciidoc content handled by Asciidoctor by way of Tilt 1.3.4
- document embedded asciidoc engine to README.md
- add asciidoctor as development dependency
Merge pull request #357 from mojavelinux/asciidoc

register embedded engine for asciidoc
readme cleanup

[ci skip]
changes

[ci skip]
Make Regexp.union work with both 1.8.6 and 1.8.7.
Unicode tag names are fully supported only in 1.9+.
Merge branch 'master' into smart_text
Merge remote-tracking branch 'rax/smart_text' into smart-text

Conflicts:
	test/smart/test_smart_text.rb