Add `AssignLocal` method to `Node` class.

This is same as the `Assign` method but uses only local variable scope,
not scope chain.
Bug fix: While loop was missing `end while`.
Add for statement.
Refactor file structure for CGI related stuff.

Move all CGI related stuff into their own subfolder to prevent directory
listing from growing even larger and to make `CgiRequest` and
`CgiResponse` classes reusable for upcoming FastCGI server API.
Disable CRLF on Windows platform.

This is common fix for CGI-programs I found from somewhere (can't
remember where) which disables CRLF-conversion on Windows platform.
Merge pull request #13 from peelonet/for-statement

For statement
Merge pull request #15 from peelonet/cgi-code-refactoring

Refactor file structure for CGI related stuff.
Add query string parsing -function.
Add new `AsString` method for `Value` class.

It can be used to ensure that an value is string.
Add initial request and response APIs.