Fix json schema generation

• Fix json schema generation as of #19
• Fix for not initialized ManyToMany relations in fastapi copies of ormar.Models
• Update docs in regard of fastapi use
• Add tests to verify fastapi/docs proper generation
• Modify schema so that ManyToMany fields show list of nested models in fastapi schema

Added name parameter to provide alternative database column names

Added possibility to provide alternative database column names with name parameter to all fields.
Fix bug with selecting related ManyToMany fields with fields() if they are empty.
Updated documentation

check the documentation: https://collerek.github.io/ormar/models/#fields-names-vs-column-names

Publish docs

Publish documentation and update readme

Add fields() QuerySet method, UUID field and UniqueColumns constraint

Add fields() method to limit the selected columns from database - only nullable columns can be excluded.
Added UniqueColumns and constraints list in model Meta to build unique constraints on list of columns.
Added UUID field type based on Char(32) column type.

For details check Readme and tests.

Add bulk operations

Added bulk_create and bulk_update for operations on multiple objects.
See readme file and tests.

Add queryset level methods

Add queryset:

• delete
• update
• get_or_create
• update_or_create

Add additional filters - startswith and endswith

Like described in encode/orm#49 - additional filter operators using like and ilike under the hood

Add choices param

similiar to one described in encode/orm#57

Added exclude, more fixes and tests

Added exclude to filter where not conditions.

Added tests for mysql and postgres with fixes for postgres.

Rafactors and cleanup.

Added Many2Many relations

Merge pull request #4 from collerek/many_to_many

Many to many