Expose module.exports to tiddler modules

Needed to incorporate an upcoming third-party library.

@natecain - do you think this is OK from a compatibility perspective?
Move startup.js into the startup folder

Neater.
Introduce info mechanism

We expose browser information as shadow tiddlers so that wiki
applications can adapt to available features.
Start refactoring tw5.com GettingStarted content
Move info mechanism docs to correct place
Make default location for new tiddlers configurable
Merge remote-tracking branch 'upstream/master'