Rename text to nodeText in DOMNode(Text) category

The -text signature is already used in various subclasses (e.g.
DOMScriptElement).
Do not use textContent to get inner text

According to specification, textContent includes everything in the
target's children, including script and style tags.[1] Even jQuery
recognise that using it in their .text() implementation is a bug,
although they (FWIW) refuse to fix it.[2]

Other options, most importantly using innerText instead, also have
their own set of problems, as described in a relevant Mozilla
document.[3]

The current implementation ditches all the above. We now traverse
child nodes ourselves, and implement custom logic to explicitly
exclude SCRIPT and STYLE tags.

This should behave very similarly to textContent except for SCRIPT
and STYLE tags. Anything that does not conform to specification of
textContent should be considered as a bug.
Merge branch 'fix_80_word-count'

Fix #80