Fix TOML 1.0.0 compliance

.coveragerc

@@ -1,3 +1,2 @@
 [run]
 omit = tomlkit/_compat.py,
-

.flake8

@@ -0,0 +1,17 @@
+[flake8]
+max-line-length = 88
+ignore = E501, E203, W503
+per-file-ignores = __init__.py:F401
+exclude =
+    .git
+    __pycache__
+    setup.py
+    build
+    dist
+    releases
+    .venv
+    .tox
+    .mypy_cache
+    .pytest_cache
+    .vscode
+    .github

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "tests/toml-test"]
 	path = tests/toml-test
 	url = https://github.com/BurntSushi/toml-test.git
+[submodule "tests/toml-spec-tests"]
+	path = tests/toml-spec-tests
+	url = https://github.com/iarna/toml-spec-tests.git

.pre-commit-config.yaml

@@ -1,6 +1,22 @@
 repos:
--   repo: https://github.com/ambv/black
+  - repo: https://github.com/ambv/black
     rev: stable
     hooks:
     - id: black
       python_version: python3.6
+
+  - repo: https://github.com/timothycrosley/isort
+    rev: 5.1.4
+    hooks:
+      - id: isort
+        additional_dependencies: [toml]
+        exclude: ^.*/?setup\.py$
+
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.1.0
+    hooks:
+      - id: trailing-whitespace
+        exclude: ^tests/(toml-test|toml-spec-tests)/.*
+      - id: end-of-file-fixer
+        exclude: ^tests/(toml-test|toml-spec-tests)/.*
+      - id: debug-statements