Update README.

- Updates the JSON example to account for the new capability of testing a
cue's cuetext.
- Adds the new convertCueToDOMTree() parser function to the API list.
Fix README to have convertCueToDOMTree as code markup.
Move cue setting line tests over to test.list files.
Move cue setting position tests to test.list files.
Disable streaming tests due to exceeding max call stack.
Change percentage values to be stored as numbers.

We were storing percentage values as strings with [num]%. The spec
says to store these as numbers instead. In the case of line, which
can be an integer or a percentage, we have to differentiate between
the two with the snap-to-lines flag. We have to expose this in the
WebIDL as well so we have to do the conversion at some point. I think
it's best to just store it as a number right off the bat.
Remove cue-settings-position.vtt.

This should have been removed when the test was switched over to
work with the new test.list files.
Move cue setting size tests over to new test.list files.
Move bold span tests to new test.list files.
Merge pull request #18 from RickEyre/new-tests-two

Moving tests to test.list files
Move cuetext class span tests to test.list file
Fix class list on cues to be separated by spaces.

Comment in the code is correct so this was a typo in the code.
Move voice span tests to new test.list files.
Make annotations on valid tags be optional.

Annotations on voice tags and lang tags get set to an empty string
if there is no annotation.

See http://dev.w3.org/html5/webvtt/#webvtt-cue-text-parsing-rules
Move italic span tests to new test.list files.
Move underline span tests to new test harness.
Move cuetext lang span tests to new test harness.
Move cuetext ruby span tests to new test harness.
Rt tags need need to be a child of a ruby tag.

Rt tags need to be the child of a ruby tag in order to be
considered valid. I've added a shouldAdd() function whose
purpose is to determine if the node is valid based on the
context of where it appears in the cuetext.