text: Title: script_location PATH config is not OS agnostic
  Body: **Describe the bug**
  This setting is different if you are running on Windows OS or Linux OS
  
  ```
  script_location = app/db/migrations
  ```
  
  **Expected behavior**
  I am developing on Windows machine and i set the value of the setting to "app\db\migrations"
  
  But then I build docker image, deploy and want to run it the server and I have to fix the config file to "app/db/migrations"
  
  I find myself changing this quite frequently, is there a way to define this with mutli OS support in mind?
  
  Thanks
  
  **To Reproduce**
  Please try to provide a [Minimal, Complete, and Verifiable](http://stackoverflow.com/help/mcve) example, with the migration script and/or the SQLAlchemy tables or models involved.
  See also [Reporting Bugs](https://www.sqlalchemy.org/participate.html#bugs) on the website.
  
  ```py
  # Insert code here
  ```
  
  **Error**
  
  ```
  # Copy error here. Please include the full stack trace.
  ```
  
  **Versions.**
   - OS: 
   - Python:
   - Alembic:
   - SQLAlchemy:
   - Database:
   - DBAPI:
  
  **Additional context**
  <!-- Add any other context about the problem here. -->
  
  **Have a nice day!**
  