update README.md
update gradle to v2.0 and add language version variables
add vertx-langs to dependencies list
fix 'runMod' task

Prevent 'No such property: args for class: org.gradle.api.DefaultTask_Decorated' message. `args` is not a property of gradle task, but should be local value instead.
change sonatype repository url to https to avoid redirect bug
add 'vertx_classpath.txt' to .gitignore
update README.md
update build scripts to gradle 2.0