Inline guard in api.ts

[lynn]

I think this is a case where duplication is cheaper than the wrong abstraction. Not that guard() is wrong per se, but explicitly writing out each check will make the API functions easier to type (in the TypeScript sense) and easier to follow (less "callback hell" / it's completely clear what gets checked where in what order).

This will also help turn this file into a (testable!) ToaduaApi class. Right now checks.goodid depends on index_of which depends on store which is a global. Eventually it'll want to be something like this.goodid which uses this.store. And this refactor will be easier to reason about without having to deal with the overly-abstract guard.

For now, I've just tried to mechanically repace every entry like:

    body: checks.nobomb,

with a simple if-return like:

    const (e_body) = checks.nobomb(i.body);
    if (e_body !== true) return ret(flip(`invalid field 'body': ${e_body}`));

Hopefully, this sets up a future PR to get rid of ret() and completely eliminate the continuation-passing style from the API.

[uakci]

Changes look good, thanks for the contribution =:3!