Add eslint linter (#52)

Add eslint linter (#52)

* Add eslint and configuration. it reports 114 issues

* eslint: fix spacing, semicolons, long lines, == vs ===

* eslint: remove unused variables

* eslint: allow function use before declaration. function are hoisted, so safe, and it adds to readability

* eslint: fix reused variable names (no-shadow)

* eslint: disable no-label-var rule for *.svelte files as it misreports reactive-statements