CLN: Condense PR style checklist into one script

Author: gfyoung

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,4 @@
 - [ ] closes #xxxx
 - [ ] tests added / passed
-- [ ] passes `black pandas`
-- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
+- [ ] passes `./scripts/quick_style_check.sh`
 - [ ] whatsnew entry

scripts/quick_style_check.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+lint_files() {
+    git diff upstream/master --name-only -u -- "*.py" | xargs -r $1
+}
+
+echo "FLAKE8 check: it passes if no errors are reported"
+echo ""
+
+lint_files flake8
+
+echo ""
+echo "ISORT check: it passes if no files need to be fixed"
+echo "If fixes are made, please commit those with your changes"
+echo ""
+
+lint_files isort
+
+echo ""
+echo "BLACK check: it passes if no files need to be reformatted"
+echo "If reformats is done, please commit those with your changes"
+
+lint_files black