CheckColumns Constraint (#730)

* feat: add check columns class

* feat: write document of check columns part

* test: write a test for check columns constraints

* fix: debuging test exception raise mysql

* fix: set pragma no cover to ignore cov

* fix: ignore pytest raise in python 3.x not 10

* feat: set constraint name for check columns

* refactor: support index and check overwrites

* fix: debuging check constraint arguments

* fix: debug coverage all code tests

* fix: pass the map of type constraint to counter

* refactor: edit check name replace sapce underline

* refactor: write new function copy constraints

* test: write test for invalid constraint type

* fix: debug text cluase replaced names

* fix: set pragma no cover for result returned

* refactor: no coverage for main if statement

* perf: change get constraint copy func code

* fix: fix bug in mypy typing check

docs_src/models/docs018.py

@@ -0,0 +1,25 @@
+import datetime
+import databases
+import sqlalchemy
+
+import ormar
+
+database = databases.Database("sqlite:///db.sqlite")
+metadata = sqlalchemy.MetaData()
+
+
+class Course(ormar.Model):
+    class Meta:
+        database = database
+        metadata = metadata
+        # define your constraints in Meta class of the model
+        # it's a list that can contain multiple constraints
+        # hera a combination of name and column will have a level check in the db
+        constraints = [
+            ormar.CheckColumns("start_time < end_time", name="date_check"),
+        ]
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=100)
+    start_date: datetime.date = ormar.Date()
+    end_date: datetime.date = ormar.Date()