[#2272] Added split function to expression syntax

doc/sphinx/arm/classify.rst
    Documented new split() function

src/lib/eval/eval_messages.cc b/src/lib/eval/eval_messages.*
    New debug log messges

src/lib/eval/lexer.ll
src/lib/eval/parser.yy
    added split parsing

src/lib/eval/tests/token_unittest.cc
    Added tests for split()

src/lib/eval/token.*
    Added TokenSplit class

doc/sphinx/arm/classify.rst

@@ -474,6 +474,10 @@ Notes:
    |                       |                         | a hexadecimal string, |
    |                       |                         | e.g. 0a:1b:2c:3e      |
    +-----------------------+-------------------------+-----------------------+
+   | Split                 | split('foo.bar','.',2)  | Return the second     |
+   |                       |                         | field, splitting on   |
+   |                       |                         | dots.                 |
+   +-----------------------+-------------------------+-----------------------+
 
 .. table:: List of conversion-to-text expressions
 
@@ -586,6 +590,25 @@ or:
 
            'abcdefghijkl...'
 
+Split
+---------
+
+The Split operator ``Split(value, delimiters, field-number)`` accepts a list
+of characters to use as delimiters and a positive field number of the
+desired field when the value is split into fields separated by the delimiters.
+Adjacent delimit are not compressed out, rather they result in
+an empty string for that field number.  If value is an empty string, the result
+will an empty string.  If the delimiters list is empty, the result will be the
+original value.  If the is less than one or larger than the number of fields,
+the result will be an empty string. Some examples follow:
+
+::
+           split ('one.two..four', '.', 1) == 'one'
+           split ('one.two..four', '.', 2) == 'two'
+           split ('one.two..four', '.', 3) == ''
+           split ('one.two..four', '.', 4) == 'four'
+           split ('one.two..four', '.', 5) == ''
+
 Ifelse
 ------