upgrade JRuby and JRuby plugin

- upgrade JRuby to 1.7.17
- upgrade JRuby plugin to 0.1.10
- tweak Gradle build to allow tests to be run on JDK6
- reenable openjdk6 in build matrix
Merge pull request #241 from mojavelinux/jruby-upgrade

upgrade JRuby and JRuby plugin
add config file for appveyor
Merge pull request #245 from mojavelinux/appveyor-config

add config file for appveyor
show test results in console output when info is enabled

- show test results in console when info is enabled
- add JDK 1.7.0 to build matrix on AppVeyor
- set TERM=dumb when running builds on AppVeyor
update AppVeyor config
set PATH correctly in AppVeyor config
tidy up build scripts

- separate out common logic for distribution and non-distribution builds
- move library versions to top-level ext block
- enable sources & javadoc for all jar archives
- move sourceCompatibility & targetCompatibility to gradle.properties
add AppVeyor badge to README
Merge pull request #238 from mojavelinux/build-updates

tidy up build scripts
make note about the TMP or TEMP environment variable
Update appveyor.yml with gradlew coordinates

Let's print out the current gradle version too, just to be sure we have the right environment for a build
Merge pull request #248 from aalmiray/patch-2

Update appveyor.yml with gradlew coordinates
Fix to allow extensions from non-"com." packages to be registered
Resolves #250, including test which fails without this fix
Merge pull request #251 from ktoso/fix-extension-importing-ktoso

Fix to allow extensions from non-"com." packages to be registered
Merge branch 'master' of https://github.com/asciidoctor/asciidoctorj
code review for converters API

- name interface Converter instead of ConverterBuiltIn
- only add necessary methods to Converter API
- add required constructor to TextConverter
- cleanup converter test
adds AbstractConverter class.
creates AbstractNode class.
Merge branch 'converters' of https://github.com/asciidoctor/asciidoctorj into converters