operator functionality in CQL

Intention: Allow operators in CQL

Operators could be decimal arithmetics + - * / or boolen arithmetics | & ! or string 'arithmetics' +

SELECT tab.label + ' = ' + tab.value FROM foo.tab
SELECT * FROM tab WHERE tab.label + ' = ' + tab.value = 'foo = bar'
as well as
CREATE INDEX idx ON tab ( tab.tabel + '=' + tab.value )
or
CREATE INDEX idx ON tab (label) WHERE contains(tab.tabel, 'very-important-key')

Operators could be mapped to UDFs like this:
+ mapped to UDF cstarstd::oper_plus(...)
- mapped to UDF cstarstd::oper_minus(...)
or handled directly via Cql.g in 'special' code