README, LICENSE and .gitignore refresh

- ignore bin directories for those that `bundle install --binstubs`
- ensure Markdown files are rendered that way on Github
- refresh README.md with svg badges and ensuring Supported Ruby Versions are front and centre
use gem name specifically
ensure badges are above the fold for more glance-ability
more confident ruby version support
document development installation instructions too
include more installation options
Merge pull request #87 from karlfreeman/readme-license-gitignore-refresh

README, LICENSE and .gitignore refresh