Parse SQL script files using external lib

[amochin]

Fixing #184, I slightly improved splitting the SQL script files into statements - now some more statements blocks of a PL/SQL script for Oracle are processed correctly. However, I found out that I was just scratching on the surface.

There are so many different statements, operators and SQL dialects, that there are extra projects, dedicated to splitting a script file into a list of statements.
There is one, which I tried - sqlparse.

It worked pretty well for a SQL script with multiple PL/SQL blocks for MSSQL.
It wasn't so good with a script for Oracle though (see create_stored_procedures script files in the tests folder).
Anyway, it might be reasonable to with the current implementation of the Execute SQL Script keyword to using this external parser - and improve parsing Oracle scripts directly there.