Compatibility with es module implementations

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As hyogwa intended to be used with bundlers, hyogwa works well with them. However, I've reported and saw some problems of using hyogwa directly in the node/browser environment after compiling the program with tsc. In this issue, I'm going to investigate environments/settings where using hyogwa is hard or impossible and try to find best solution.

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If you have any problem of using hyogwa in your project, please report the problem in this issue.

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It seems most issues are solved by #33 but I'll keep this issue open for a while since there might be other problems.

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I found an issue while I try to import hyogwa on Deno using deno.land. Seems to be module resolution problem with file extension.

I tried to import hyogwa with `import * Hyogwa from 'https://deno.land/x/hyogwa@v0.1.0-rc.4/src/index.ts' but accidentally faced this error:

error: Module not found "https://deno.land/x/hyogwa@v0.1.0-rc.4/src/core.js".
    at https://deno.land/x/hyogwa@v0.1.0-rc.4/src/index.ts:7:100