`Accept` header parsing utilities

[aquapi]

Support Accept header parser, which also include parsing for Accept-Language and Accept-Encoding.

Proposed API:

// Returns the value or null/undefined (benchmark later)
const parseHeader = parseAccept('Accept-Language', ['en', 'ja', 'zh']);

app.get('/', (c) => c.send(parseHeader(c) ?? 'en'));

[aquapi]

Some optimizations can be done with this: https://developer.mozilla.org/en-US/docs/Glossary/Quality_values

[aquapi]

Added in commit: 22c6bb5

import accept from 'zesti/utils/fast-accept';

const parseAccept = accept(
  'Accept-Language',
  ['en', 'ja', 'zh'],
  'en'
);

app.get('/', (c) => {
  const lang = parseAccept(c); // 'en', 'ja' or 'zh'
  return c.send('Supported language: ' + lang);
});

Note that this is only standard-compliant for Accept-Language and Accept-Encoding.

I will need a better implementation for Accept later.

[aquapi]

Implementation note:

'a/b' = q * 1
'a/*' = q * 0.999
'*/*' = q * 0.9989

For other property parsing probably use JSON.parse if string is double quoted (since other ways of doing this are either incomplete or slower)