Make it easier to add new matching methods

[roquelopez]

Currently all the algorithms for schema and value matching are grouped into a single module (algorithms.py). Ideally, each algorithm should be in a different module under a common package (e.g. . If external contributor want to add new methods, they just would need to create a new module.

Also, move SchemaMatchers and ValueMatchers (Enums) to __init__.py of this common package.