Support table_options on ManyToMany intermediate tables

[guest]

Need way to support table_options on intermediate tables created from ManyToMany relationships. eg: defining an InnoDB engine for MySQL databases, which for most tables can be done with using_table_options(mysql_engine="InnoDB"), however an equivalent option is not available for intermediate tables created from ManyToMany relationships.

A couple possible solutions:

1. add an argument like "table_kwargs" and implement for ManyToMany
2. implement support for default table_options in ManyToMany so that elixir.options_defaults['tables_options'] = dict(mysql_engine="InnoDB") could be used

These solutions were originally suggested in the Elixir Forum Thread: Using InnoDB Engine for ManyToMany Relationships

[ged]

table_kwargs done in r477

[ged]

options_defaults done in r478, r479.