Remove special "only text" handling for textarea, code and friends

[Suor]

Now it is impossible to write any jade code in these tags, like:

textarea#code
  include code_sample.html

It is so simple to add . after all, no need to mess with special casing.

[tj]

yeah, text-only was added really early on but in general I could agree now that we have the trailing ., though I do think it's more intuitive to have some tags default to text-only, inconsistency is certainly an argument