Opt-in ESLint config

[tukib]

Problem

Writing and reviewing correct code can be more efficient with the use of ESLint. However, this could slow down contributors who are unfamiliar with ESLint rules, and we have not yet identified a good reason to require it.

Context

Configure an opt-in ESLint config for our project. This will follow from:

• we have no linting configuration (ESLint proposal) #58
• we have no type safety for linting (TypeScript proposal) #59
• stricter linting/typing configurations #60

we will check in .eslintrc rules for the whole thing. and then we will control which files are required to conform to it (opt in) in the eslintignore file.

old proposal

We could check in a template config (e.g. template.eslint.rc) and add the real config to gitignore (e.g. .eslintrc). We will not add ESLint to the package.json lint script.~~

• Then by default, neither code editors nor the lint PR check will use this.
• To opt-in, a contributor can copy the template.

[seanmakesgames]

we will check in .eslintrc rules for the whole thing. and then we will control which files are required to conform to it (opt in) in the eslintignore file.