BitMagic release v7.7.7

1.Fixed a bug in bm::bvector<>::merge() - destructive OR operation, when arg vectors is empty and uninitialized
function did not implement a correct logical OR (serious issue!)

2.Implemented a new logical idiom bvector<>::bit_or_and()
as
C := C OR (A AND B)
Fused OR+AND is an often used idiom in query systems, implementations of SQL and operation on memory compressed
structures. Fused implementation uses multiple optimizations and does not require a temporary vector, avoiding
allocations and memory copy.
New idiom is 2x times faster in synthetic tests of uncompressed bit-vectors.

3. bm::aggregator::pipeline now implements a fast mode to run multiple AND-SUB queries with an optional
   aggregation of results via an OR function.

Aggregator logical pipeline implements fast idioms used in BitMagic succinct vectors to implement
sparse/dense vector search or query requests.

bm::aggregator::pipeline uses cache memory bandwidth and optimizations to implement
series of AND-SUB as: (bv1 AND bv2 AND bv3…) AND NOT (bvS1 OR bvS2 OR … ) with an optional final
accumulation of multiple search requests using OR logical function.

Aggregator pipeline is used internally in BitMagic to implement succinct bit-sliced vector searches
(bm::scanner<>) 2-3 times faster. The speed achieved in 7.7.7 release demonstrates performance levels
otherwise specific to systems using indexes.
Fast index-free searches can significantly reduce both the systems footprint (RAM and disk) and
complexity of implementation.

4. Algebra of Sets tutorial (bvsetalgebra.cpp) example reworked to illustrate use of new fused OR-AND
   operations and aggregator pipeline (AND-SUB-OR).

https://github.com/tlk00/BitMagic/tree/master/samples/bvsetalgebra

5. bm:scanner::pipeline implements fast multiple string search in memory compressed string vector with an
   optional OR stage (under the hood uses bm::aggregator<>).
   Latest version makes a change in semantics to use compile-time options to configure pipeline,
   new options result in faster code due to compile-time specialization (C++-17 is very useful there).

OR stage helps to implement a SQL idiom: Field1 IN (value1, value2… valueN) for cases where list of
search values is in the tens of thousands or more or Field1 IN (SELECT FieldN FROM…) idiom using
memory compressed index-free search.

New version adds important optimizations of the algorithms to automatically tune-up for a typical
L2 cache size, but also adds a manual override (batch_size) to tune and tweak the system for a specific
HW configuration and data distribution statistics. The auto-tune topic definitely deserves more optimization
in the future.

New usage modes and benchmarks are available at:
https://github.com/tlk00/BitMagic/tree/master/samples/strsvsample07

Release notes:
http://bitmagic.io/bm-7.7.7.html