Update README, CHANGELOG, Travis config for 3.5

Author: apotterri

.travis.yml

@@ -1,5 +1,7 @@
 language: python
-python: "3.9"
+python: 
+- "3.5"
+- "3.9"
 
 stages:
 - lint
@@ -18,7 +20,7 @@ jobs:
   - stage: lint
     script:
     - poetry run pylint appmap
-    - poetry run vermin -t=3.7- appmap
+    - poetry run vermin -t=3.5- appmap
   - stage: test
     script:
     - poetry run pytest -svv

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Changed
+- Relax the python version requirement to 3.5.
+
 ### ## [0.1.0.dev8] - 2021-02-22
 - [#27] Capturing HTTP requests and responses when testing Django apps.
 
@@ -107,7 +110,7 @@ testing. Also adds a Travis config to run them all.
 
 
 [Unreleased]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev8...HEAD
-[0.1.0.dev8]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev67...0.1.0.dev8
+[0.1.0.dev8]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev7...0.1.0.dev8
 [0.1.0.dev7]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev6...0.1.0.dev7
 [0.1.0.dev6]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev4...0.1.0.dev6
 [0.1.0.dev4]: https://github.com/applandinc/appmap-python/compare/0.1.0.dev3...0.1.0.dev4

README.md

@@ -30,8 +30,8 @@ The second option is to upload them to the [AppLand server](https://app.land) us
 
 ### Supported versions
 
-* Python 3.9
-* Pytest 6.2
+* Python >=3.5
+* Pytest >=6.1.2
 
 Support for new versions is added frequently, please check back regularly for updates.
 
@@ -240,6 +240,14 @@ you can generate a recording of the code
 
 [![Build Status](https://travis-ci.com/applandinc/appmap-python.svg?branch=master)](https://travis-ci.com/applandinc/appmap-python)
 
+### Python version support
+As a package intended to be installed in as many environments as possible, appmap-python
+needs to avoid using features of python or the standard library that were added after the
+oldest version currently supported (see [above](#supported-version))
+
+While we use `vermin` to try to detect the use of newer features, it's easily
+fooled. When making changes, please respect the version requirement.
+
 ### Dependency management
 
 [poetry](https://https://python-poetry.org/) for dependency management: