feat(loader): scan for config keys files

[ineshbose]

attempts to resolve #137

file tree example:

tailwind.config.js
tailwind.theme.config.js
tailwind.theme.extend.config.js
.config/tailwind.config.js
.config/tailwind.js
.config/tailwind/theme.js
.config/tailwind.theme.js
.config/tailwind.theme.config.js
.config/tailwind/theme.config.js
.config/tailwind/theme/extend.js

(re-pointing source branch from #210)