resolves #597 support quoted index terms that may contain commas
resolves #653 build gemspec files using git ls-tree

- build gemspec files using git ls-tree
- remove gemspec task in Rakefile
- code formatting
Merge pull request #652 from mojavelinux/issue-597

resolves #597 support quoted index terms that may contain commas
Merge pull request #655 from mojavelinux/issue-653

resolves #653 build gemspec files using git ls-tree
resolves #654 use gem tasks from Bundler

- use bundler/gem_tasks for build, release and install
- delegate console task to Bundler
- fix warning in gemspec
Merge pull request #656 from mojavelinux/issue-654

resolves #654 use gem tasks from Bundler
resolves #630 add hardbreaks option to block

- add hardbreaks option to block (emulate ' +' at end of line)
- cleanup some attribute lookups
Merge pull request #657 from mojavelinux/issue-630

resolves #630 add hardbreaks option to block
resolves #549 added sectnumlevels to control depth of section numbering
Merge pull request #660 from mojavelinux/issue-549

resolves #549 added sectnumlevels to control depth of section numbering
resolves #636 ensure Extensions constant is Asciidoctor::Extensions
Merge pull request #665 from mojavelinux/issue-636

resolves #636 ensure Extensions constant is Asciidoctor::Extensions
compat library for Opal
opal constant
replace '[:blank:]' pattern with ' \t'
replace '[:alnum:]' pattern with 'a-zA-Z0-9'
replace '[:alpha:]' pattern with 'a-zA-Z'
replace '[[:digit:]]' pattern with '\d'
Merge pull request #667 from Mogztter/opal-constant

Introduce OPAL constant to indicate whether the Ruby engine is Opal.
split opal/compat.rb into multiple files, move to opal_ext