Added normalize() field operator

I get your code and converted in a field operator. I preferred to call
the funtion "normalize" because everywhere I find this name, even in
the spec: http://www.unicode.org/reports/tr15/tr15-23.html

Syntax

<field>.normalize( [<form>] [,<pattern-matching>] )

where:
<form> can be NDF, NFD, NFKC, NFKD. Default is NDF.
<pattern-matching> if not defined is "\\p{InCombiningDiacriticalMarks}+"
Examples:

select name.normalize() from Account limit 1
select name.normalize('NFD') from Account limit 1