Ignore file support

[tj]

There will of course be .upignore support, but I'd love some feedback on default behaviour:

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• add filter support
• add .gitignore if present
• add .npmignore if present

[hhsnopek]

Will .upignore allow inverse/negative-patterns and override previously defined patterns if other ignores files, like dotfiles/.gitignore, are allowed/used?

[tj]

@hhsnopek yep! For now I'm going to ignore dotfiles by default, and combine .gitignore/.npmignore/.upignore (in that order), but ! is supported

[tj]

pretty unintuitive when .gitignore usually has node_modules, guess we'll have to inject that in all hacky like :'(

[hhsnopek]

if up has a "starter-kit" for node, add it to the .upignore, and add a note in the docs 🙃

[tj]

injecting it in there for now :D haha, can still override via .upignore if anyone is using webpack etc, kinda hacky but definitely what I'd expect.