Configure isort and towncrier, fix Flake8 config

Configure isort to recognise CCTBX imports and run it as a pre-commit
hook.

Flake8 is no-longer available as a pre-commit out-of-the-box hook.
Update accordingly.  See
https://github.com/pre-commit/pre-commit-hooks#deprecated--replaced-hooks

.pre-commit-config.yaml

@@ -1,21 +1,33 @@
 # Run libtbx.pre-commit install to enable repository pre-commits.
 repos:
 
-# Automatic source code formatting
+# Automatically sort imports with isort
+- repo: https://github.com/timothycrosley/isort.git
+  rev: 4.3.21-2
+  hooks:
+  - id: isort
+    additional_dependencies: [toml]
+
+# Automatic source code formatting with Black
 - repo: https://github.com/psf/black
   rev: 19.10b0
   hooks:
   - id: black
     args: [--safe, --quiet]
 
-# Syntax check and some basic flake8
+# Enforce style with Flake8
+- repo: https://gitlab.com/pycqa/flake8
+  rev: 3.8.3
+  hooks:
+  - id: flake8
+    args: ['--max-line-length=88', '--select=E401,E711,E712,E713,E714,E721,E722,E901,F401,F402,F403,F405,F631,F632,F633,F811,F812,F821,F822,F841,F901,W191,W291,W292,W293,W602,W603,W604,W605,W606']
+
+# Syntax check with pre-commit out-of-the-box hooks
 - repo: https://github.com/pre-commit/pre-commit-hooks
-  rev: v2.0.0
+  rev: v3.1.0
   hooks:
   - id: check-ast
   - id: check-yaml
-  - id: flake8
-    args: ['--max-line-length=88', '--select=E401,E711,E712,E713,E714,E721,E722,E901,F401,F402,F403,F405,F631,F632,F633,F811,F812,F821,F822,F841,F901,W191,W291,W292,W293,W602,W603,W604,W605,W606']
   - id: check-merge-conflict
   - id: check-added-large-files
     args: ['--maxkb=200']

pyproject.toml

@@ -0,0 +1,14 @@
+[tool.towncrier]
+package = "screen19"
+package_dir = ".."
+filename = "CHANGELOG.rst"
+
+[tool.isort]
+known_cctbx="boost,boost_adaptbx,cbflib_adaptbx,cctbx,chiltbx,clipper_adaptbx,cma_es,cootbx,crys3d,cudatbx,fable,fast_linalg,fftw3tbx,gltbx,iota,iotbx,libtbx,mmtbx,omptbx,prime,rstbx,scitbx,simtbx,smtbx,spotfinder,tbxx,ucif,wxtbx,xfel"
+sections="FUTURE,STDLIB,THIRDPARTY,CCTBX,FIRSTPARTY,LOCALFOLDER"
+# Explicitly black-compatible settings
+multi_line_output=3
+include_trailing_comma=true
+force_grid_wrap=0
+use_parentheses=true
+line_length=88