Fix exports

[trxcllnt]

• Adds the missing extensions to the includes and ignoreerror exports
• Adds/renames the top-level exports so they match the directory names.
• Ensures UMD exports align with the exports for the other packages

With these changes, all the following forms are now valid:

import * as it from 'ix/iterable';
import * as ai from 'ix/asynciterable';
import * as itOps from 'ix/iterable/operators';
import * as aiOps from 'ix/asynciterable/operators';

Before, the only way to import all exports (across all published packages) was to import from the top-level:

import * as itOps from 'ix/Ix.iterable.operators';

Closes #370