Refactoring Zengine

Goal is: migrate Z from being a _static_ execution context => becoming a instance one.

This might include migrating things out of Z to keep it abstract parent for Q,L and other family.
Idea is to keep API as simple as possible:

```java
result = new Q("select text from myTable")  // load some data
                      .pipe(new L("wordcount"))     // load wordcount library
                      .execute()                            // execute
                      .result();

result.write(System.out);                             // Print result to stdout
```