add pre-commit hook

validate-hook - add envars-validate hook (#33)

Description: Added envars-validate pre-commit-hook to run the validate
command off the repository, to support our other pre-commit stacks

Ticket: tops-1718

Testing: Used via the personal test repository targetting branch

TOPS-688 - migrate to Invoke

migrate from make to invoke (#30)

- Migrate to use Python Invoke 
- Update README 
- Update version number

TOPS-1015 - Update pip dependencies

update envars version number (#29)

This is so that a Github release number matches a package version. 

- Drops support for python < 3.8
- Also made some small updates to setup.cfg.

0.7: TOPS-656 - enable override of env check (#24)

in some rare cases the value of stage is dynamic

0.6: TOPS-656 - fix default template vars (#23)

broken in a previous refactor

add set-systemd-env

TOPS-656 - single rather than double quote (#19)

preserve the literal value of all characters in bash

exec and bugfixes

TOPS-656 - fix = in vars for exec (#17)

`=` and anything after it was drop from variable values when using exec

exec isn't actually used anywhere in prod yet

0.3: TOPS-656 - exec support STAGE/RELEASE_SHA from env (#11)

when used in AMI apps the STAGE and RELEASE_SHA are set by system
environment variables

0.2: TOPS-656 - support parameter store values (#8)

in rare cases (gp-web canary) the value of an envar can't be determined
until runtime, this commit enables a var to be loaded from parameter
store at runtime.

Ticket: TOPS-656

Testing: added a test and will test on gp-web in Sandbox

MVP

TOPS-656 - fix refactor and add more tests (#4)

#3 broke printing