XQuery 3.1: Better support for XQuery Update

[ChristianGruen]

Allow more expressions to be updating:

…provided that XQUF 1.0 constraints will not be violated.

1. Example (works already in BaseX 8.x):

(<a/>, <b/>) ! fn:put(., name() || '.xml')

2. Example:

copy $c := <a/>
modify (insert node "A" into $c)
return fn:put($c, 'result.xml')

Introduce new Updating Module

Updating variants of higher-order functions:

• update:apply
• update:for-each
• update:for-each-pair
• update:map-for-each

Other functions:

• update:output (before: db:output)
• update:output-cache (before: db:output-cache)

[ChristianGruen]

Documentation Update Module: http://docs.basex.org/wiki/Update_Module