document regexp scalar functions
add regexp operator ~ docs
improve regex functions docs
add ``regexp_matches`` scalar function implementation
add ``regexp_replace`` scalar function implementation
implemented parser support for regexp operator ~
implemented regexp match operator
replace BytesRefInput and BooleanInput with Literals
added test for regex functions on non-indexed and fulltext indexed columns
fixed NPE on new boolean literal creation
fixed regex index type variation tests
implemented subscript array notation support
(only 1 array element supported at nested subscript tree)
return NULL on array out of bound access instead of throwing an exception
new snapshot version