Refactor getExportPaths

[huozhi]

x-ref: #228 (review)

One design improvement could be: keep getExportPaths simple, that reciving a resolved exports map instead of cwd and doing cwd operation

[devjiwonchoi]

Do you mind if I set this as experimental, add console warn something like:

Warning: wildcard export "./*" is experimental and may change or be removed at any time.
To submit an issue, please visit https://github.com/huozhi/bunchee/issues.

It is because this feature is not yet stable and need to be more tested, and I'm thinking of wildcard support like ./...folder/*also.

[huozhi]

@devjiwonchoi sounds good! 👍 Let's add an experimental warning for this, thanks

[devjiwonchoi]

Do you prefer to use syntax highlights like chalk or none?

[huozhi]

I'd like to keep it simple for now, just using console.log

[devjiwonchoi]

In #244 I used console.warn and added test. If you want log, I can edit it:)

[huozhi]

console.warn is also fine as we stick to native logging without extra ascii colors