refactory solcjs module

[alincode]

@todo

• modularize compiler code
• minimize code
• implement module API as specified below

---

Is your feature request related to a problem? Please describe.

• it should be able support all version, and easy to expand.

Describe the solution you'd like

• split big function, make it more easy to testable
  • Ask Stack: Is it OK to split into small functions, even if they’re called once?
• add test case
• use promise wrap public function

Describe alternatives you've considered

Additional context

@serapath advice todo

1. solcjs.version2url --->  await solcjs.versions
2. solcjs ---> await solcjs
3. compiler ---> await compiler
4. add compiler.version function return { name: '', url: ''}

[serapath]

haha :-) when you click new issue there is a small link below Don’t see your issue here? Open a regular issue. which allows you to open an issue without a template.

[serapath]

I checked your modules:

1. i like those:
   https://www.npmjs.com/package/ajax-caching
   https://www.npmjs.com/package/solc-version

2. not yet sure - need to see an example how they work with the compiler import callback
   https://www.npmjs.com/package/solc-import
   https://www.npmjs.com/package/solc-resolver
   (also how they would look like if they would use many small resolver modules for each backend (e.g. swarm, github, ipfs, etc...)

3. i wish this one would be much more raw and minimal:
   https://www.npmjs.com/package/solcjs-core

4. I am not yet sure about this one - depends on solcjs-core which would be cool if it was more minimal
   https://www.npmjs.com/package/solcjs-lightweight

[alincode]

@serapath

implement a small resolver module

const ResolverEngine = require('solc-resolver').ResolverEngine;
let resolverEngine = new ResolverEngine();
let resolveGithub = require('resolve-github');
resolverEngine.addResolver(resolveGithub);
let resolveIpfs = require('resolve-ipfs');
resolverEngine.addResolver(resolveIpfs);

const getImportContent = async function (path) {
  return myDB.has(path) ? myDB.get(path) : await resolverEngine.require(path);
};

let output = await compiler(sourceCode, getImportContent);