rename attribute_value to unquoted_attribute_value etc

[milahu]

this makes my life easier when using this parser in an AST transformer

the problem is that currently, attribute_value has 2 meanings:

• attribute_value
• quoted_attribute_value
  • singlequote, attribute_value, singlequote
  • doublequote, attribute_value, doublequote

i want to process only the parent nodes attribute_value and quoted_attribute_value and ignore the child nodes: singlequote, doublequote, attribute_value

but currently, both parent and child nodes have the same node.kind_id

i propose to change this to

• doublequoted_attribute_value
• singlequoted_attribute_value
• unquoted_attribute_value

similar to #89

maybe

group the three attribute value types under one attribute_value

• attribute_value
  • doublequoted_attribute_value
  • singlequoted_attribute_value
  • unquoted_attribute_value

fixme

noval= bool is parsed as one attribute when it should be parsed as two attributes

fix: disallow whitespace between nodes

<hr doublequoted="val" singlequoted='val' unquoted=val noval= bool>