Move raw alasql querying code to separate directory and put under test.

[rgwozdz]

This PR is essentially file reorganization.

• Moves the alasql filtering instance (with winnow specific method extensions) to its own directory.
• Moves the "prepared" version of the alasql filtering instance to same directory. The prepared version sets up querying method with the SQL statement precompiled and ready for passed in parameters. Note that this prepared version is not used anywhere in the repo, but is exposed as a public method. The readme does not document it - so it's origins and use are unknown.
• puts the prepared version under test.

Note: I will have a follow-up PR that put the currently untested alasql methods under test.