Merge pull request #51 from 'hotfixes-v2.26'

Error code checking was removed.
Multiple backends support was added:

* by default there are 3 backends on each node;
* you can change backends number using **backends_number** parameter.
Merge pull request #53 from 'features/multibackends'

Multiple backends support was added:
tests: mix-states test was added
Merge pull request #55 from 'features/weight-calc-algo-v2.26'

tests: mix-states test was added
Merge branch 'v2.26' into hotfixes-v2.26