Rewrite source in Typescript

[asa-taka]

Currently index.d.ts exists (very helpful, thanks), but there are some diffs between implementation and that typing.
So I propose to rewrite src/*.js in TypeScript.

Internal Design Changes

Nested clausures are flatten, now mod is a module-scope global variable.

• TypeScript couldn't generate definitions of private things (e.g. class Common inside of _setup function).
  • At first, I've tried to define module definitions by ReturnType, to keep original code shape, but got TS4025 error (ref).
• To put out members, which originally placed inside setup function, I add a singleton variable mod, like a global variable inside mcl-wasm module.
  • Because many components inside setup function depend mod on the outside scope of them.
  • The new mod varialbe will be initialized after mcl.init() call, thus it doesn't leads braking changes for users.

Braking Changes (maybe nothing)

For JavaScript Users

Nothing. I've confirmed:

• Exported member names are identical during this changes
• All tests are passed
• Browser domo works

For TypeScript Users

Types are refactored. I've confirmed no TypeScript errors in test/test-ts.ts.

TODO Before Merge

• Remove tmp-for-ts-migration directory
  • This shows no API changes and no performance degrading

[asa-taka]

Sorry for many rebasing. I've misunderstood this repo's manner.

[asa-taka]

@herumi Thank you for merging 🎉