Automatic model code generator for SQLAlchemy

Fork from sqlacodegen. Based off of version 1.1.5.pre2.

What's different:

• Support for Flask-SQLAlchemy syntax using --flask option. All this means:
  • SQLAlchemy class is instantiated (i.e. db = SQLAlchemy()).
  • Flask-SQLAlchemy columns are used (e.g. db.Integer).
  • Metadata is only implicit in tables
• Defaults to generating backrefs in relationships. --nobackref still included as option in case backrefs are not wanted.
• Naming of backrefs is the class name is snake_case (as opposed to CamelCase) and is pluralized if it's Many-to-One or Many-to-Many using inflect.
• Generate explicit primary joins. I deal with pretty complicated tables that need explicit primary joins.
• If column has a server_default set it to FetchValue() instead of trying to determine what that value is. Original code did not set the right server defaults in my set up.
• --ignorefk ignores special name columns (e.g. id, inserted, updated) when generating association tables. Original code requires all columns to be foreign keys in order to generate association table. Example: --ignorefk id,inserted,updated.
• NOTE: As at 2015-06-26, I removed support for dogpile caching as that aspect of code was never fully developed.