Add pyproject.toml for project

pyproject.toml:
Add a pyproject.toml for describing the project, configuring all
currently required dependencies and development dependencies.
The configuration adds entries for the code formatter black, the import
sorting tool isort and for the coverage report generation tool coverage.

pyproject.toml

+[tool.poetry]
+name = "arch-repo-management"
+version = "0.1.0"
+description = "Tools for package repository management"
+authors = ["Arch Linux <arch-projects@lists.archlinux.org>"]
+license = "GPL-3.0-or-later"
+packages = [
+  {include = 'repo_management'},
+  {include = 'tests', format = 'sdist'},
+]
+
+[tool.poetry.dependencies]
+python = "^3.9"
+pyalpm = "^0.9.2"
+
+[tool.poetry.dev-dependencies]
+tox = "^3.23.0"
+pytest = "^6.2.2"
+isort = "^5.7.0"
+mypy = "^0.812"
+flake8 = "^3.8.4"
+black = "^20.8b1"
+coverage = "^5.5"
+
+[tool.black]
+line-length = 120
+exclude = '''
+/(
+  \.direnv|
+  |\.eggs
+  |\.git
+  |\.hg
+  |\.mypy_cache
+  |\.nox
+  |\.tox
+  |\.venv
+  |\.svn
+  |_build
+  |buck-out
+  |db-write
+  |db2json
+  |dbscripts
+  |build
+  |dist
+)/
+'''
+
+
+[tool.coverage.path]
+source = "repo_management"
+
+[tool.coverage.report]
+omit = ["tests/*", ".tox/*", "db-write/*", "db2json/*", "dbscripts/*"]
+precision = 2
+show_missing = true
+
+[tool.coverage.run]
+branch = true
+command_line = "-m pytest -v tests/ -m 'not integration'"
+omit = ["tests/*", ".tox/*", "db-write/*", "db2json/*", "dbscripts/*"]
+
+[tool.isort]
+profile = "black"
+multi_line_output = 3
+
+[build-system]
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"