Several updates to XPath Expressions Module

See http://www.w3.org/MarkUp/Forms/wiki/XPath_Expressions_Module

1) Added functions xf:eval() and xf:eval-in-context() per Action-1836 (
https://www.w3.org/2005/06/tracker/xforms/actions/1836)

2) Added functions xf:matches() and  xf:replace() per Action-1813 (
https://www.w3.org/2005/06/tracker/xforms/actions/1813) 

3) Amended existing example descriptions and added example to 
adjust-dateTime-to-timezone() per Action-1805 (
https://www.w3.org/2005/06/tracker/xforms/actions/1805)

4) Fixed return type of xf:attribute() function, which claimed to return 
an element()

5) Added the frequently used but undefined namespace prefix "xf"

6) Changed example in index() and valid() functions to remove unnecessary 
xforms namespacing and add following descriptions. 

Note that <xforms:instance> remains in examples of instance() and 
current() because the examples would break if prefix removed.  Those 
examples use the best practice of putting xmlns="" on the 
<xforms:instance> element to avoid infesting the XML data with xmlns="".

7) Fixed one incorrectly placed id anchor for boolean functions.

8) Added id anchor spans for almost all functions in the spec

9) Made numerous fixes to spurious div end tags

10) Added one missing "Examples:" and removed one duplicate "Examples:"

11) Made some changes to the acknowledgements (Remaining issues: Is Steven 
Pemberton entry accurate, what do we do about past members)

12) Changed editor list :-)

Cheers,
John M. Boyer, Ph.D.
Distinguished Engineer, IBM Forms and Smarter Web Applications
IBM Canada Software Lab, Victoria
E-Mail: boyerj@ca.ibm.com 

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