Added tests for helper.combine, fixed issue with combining with null values

test/helper.js
+ added tests for combining values

lib/helper.js
+ added internal 'isObject' function, which identifies true object types (e.g. {} and not [], null)
* changed 'combine' function to use the isObject function to determine course of action
Added tests for Comment nodes
Fixed issue with Node.removeChild

* the reference to the parent element is now properly removed when invoking removeChild on any element
Changed 'toString' to provide a more elaborate name for non-element nodes
Added several convenience make options

- make test-report
- make commit-count
- make credits
- make authors-file
Added Comment tests: length, replaceData, insertData, deleteData and DOMExceptions
Moved comment tests to a file of its own
moved comment attachment and removal out of its own experiment
Merge branch 'lab_test'

* lab_test:
  moved comment attachment and removal out of its own experiment
  Moved comment tests to a file of its own
  Added Comment tests: length, replaceData, insertData, deleteData and DOMExceptions
  Added several convenience make options
  Changed 'toString' to provide a more elaborate name for non-element nodes
  Fixed issue with Node.removeChild
  Added tests for Comment nodes
  Added tests for helper.combine, fixed issue with combining with null values