[feature] xml_parser: added case default
[feature] xml_parser: more tag patterns
<tagname ... (like before)
<_ ... (any tag)
<(TrxParser) ... (parser)
<{parserExpr} ... (expression of a parser)
<x=... ... (with binding)
<...:... ... (a pattern for the namespace, and one for the name)
[feature] xml_parser: added & and ! prefixes

TODO: do the same for classic_syntax/xml_parser.trx
[enhance] xml_parser: allow bindings for & prefixed patterns
[feature] xml_parser: allow | in tag patterns

e.g. <b | u | i ... >
[fix] @xml syntax: do not take care of xhtml specific things

e.g. allows to write @xml(<br>blah</br>)
[fix] xml_parser: binding on a node pattern was not working

e.g. case a=<b />: <>{a}</>
was outputing "unbound a"
[enhance] xml_parser: allow "string {with_opa}" in tag patterns

e.g.
x = "br"
case <"{x}" ... />

/!\ since bindings are done before checking, you can actually do something like this:
case <"http://{x}.org":x=_ />
which will accept, e.g., <opalang xmlns="http://opalang.org" />
but not <opalang xmlns="http://br.org" />