[mod] RangeTable - fast lookup of a integer (IP) in a range table

This patch implements a table of ranges.  A *range* is a series of integers,
e.g. 0-10 with start value 0 and end value 10.

Start and end values are stored in a two-column table, the RangeTable.  This
table is stored in Redis in a sorted list and a ZRANGEBYSCORE query can be used
to determine if a particular integer is contained in one of the ranges in the
table.

The ZRANGEBYSCORE query scales with O(log(N)). To make it more clear: a query in
a table with 1 million ranges takes just twice as long as the query in a table
with 1000 ranges.

A RangeTable is excellent for IP ranges and ultra-fast queries to see if an
IP (which is nothing but an integer) is contained in one of the ranges of the
table.

Typical applications are e.g. large IP block lists or network ranges.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/src/searx.redislib.rst

@@ -5,4 +5,5 @@ Redis Library
 =============
 
 .. automodule:: searx.redislib
-  :members:
+   :members:
+   :member-order: bysource