Merge tag 'v0.20.0' into releases

Version 0.20.0

* tag 'v0.20.0': (742 commits)
  RLS: v0.20.0
  DOC: Whatsnew cleanup (pandas-dev#16245)
  TST: Test CategoricalIndex in test_is_categorical (pandas-dev#16243)
  TST: xfail some bottleneck on windows (pandas-dev#16240)
  DOC, TST: Document and Test Functions in dtypes/common.py (pandas-dev#16237)
  TST: Remove __init__ statements in testing (pandas-dev#16238)
  DOC: don't include all methods/attributes of IntervalIndex (pandas-dev#16221)
  PKG: Fix ModuleNotFoundError: No module named 'pandas.formats' (pandas-dev#16239)
  RLS: v0.20.0rc2
  CLN: make submodules of pandas.util private (pandas-dev#16223)
  MAINT: Remove tm.TestCase from testing (pandas-dev#16225)
  MAINT: Complete Conversion to Pytest Idiom (pandas-dev#16201)
  DOC: add whatsnew for 0.21.0
  DEPR: correct deprecation message for datetools (pandas-dev#16202)
  API Change repr name for table schema (pandas-dev#16204)
  DOC: Remove various warnings from doc build (pandas-dev#16206)
  DOC: add whatsnew for v0.20.1
  BUG: Fixed renaming of falsey names in build_table_schema (pandas-dev#16205)
  COMPAT: ensure proper extension dtype's don't pickle the cache (pandas-dev#16207)
  REF: register custom DisplayFormatter for table schema (pandas-dev#16198)
  ...

Author: yarikoptic

.github/CONTRIBUTING.md

@@ -1,15 +1,18 @@
-#### A small, complete example of the issue
+#### Code Sample, a copy-pastable example if possible
 
 ```python
 # Your code here
 
 ```
+#### Problem description
+
+[this should explain **why** the current behaviour is a problem and why the expected output is a better solution.]
 
 #### Expected Output
 
 #### Output of ``pd.show_versions()``
 
 <details>
-# Paste the output here
+# Paste the output here pd.show_versions() here
 
 </details>

.github/ISSUE_TEMPLATE.md

@@ -1,4 +1,4 @@
  - [ ] closes #xxxx
  - [ ] tests added / passed
- - [ ] passes ``git diff upstream/master | flake8 --diff``
+ - [ ] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
  - [ ] whatsnew entry

.github/PULL_REQUEST_TEMPLATE.md

@@ -19,6 +19,7 @@
 .noseids
 .ipynb_checkpoints
 .tags
+.cache/
 
 # Compiled source #
 ###################
@@ -56,6 +57,8 @@ dist
 **/wheelhouse/*
 # coverage
 .coverage
+coverage.xml
+coverage_html_report
 
 # OS generated files #
 ######################
@@ -100,3 +103,5 @@ doc/source/index.rst
 doc/build/html/index.html
 # Windows specific leftover:
 doc/tmp.sv
+doc/source/styled.xlsx
+doc/source/templates/