Closes #229

The name normalization in Tarantool can be a little bit confusing
because it has two different pipelines: for SQL and for YAML
configuration.
1. SQL allows us to use table and column names with a rule:
   the name in the double quotes is processed "as is" while
   a name without double quotes is transformed to the upper
   case. Here are the examples:

   select * from t .. -> "T"
   select * from T .. -> "T"
   select * from "T" .. -> "T"
   select * from "t" .. -> "t"

   So, the only way to get in Tarantool a name with lowercase
   characters is to wrap it with double quotes.
2. YAML configuration allows us to create distributed tables with
   the following naming convention: the name is always processed
   "as is". For example:

   t -> "t"
   T -> "T"

Previously we used a pessimistic approach with a full motion for
"not in" operator. But after some research it seems that we can use
the same logic as we do for equality and "in" operator, i.e. choose
either local, either segment or either full motion policies.

Closes #226

It was a wrong assumption that `a <> 1 and a <> 2)` is equal to
`(a, a) <> (1, 2)`. Fixed.

As a side effect some refactoring was made to deal with code
duplication in the cartridge, mock and bench engines.

Previously, only the table cache was invalidated on the router. Now
we flush cached IRs as well.

Thanks to the updates in tarantool module we don't use tarantool
symbols to work with decimal. As a bonus we can remove our mocking
framework with dynamic linking of the decNumber library to cargo
test binary.