Add back docs for readFile() and writeFile() which got removed from README.
Merge pull request #19 from humphd/develop

Add back docs for readFile() and writeFile() which got removed from README
Update README.md
Minor corrections for README.md -- fs.rename, "agruments" typo, fs.link param names
Merge pull request #27 from skaegi/develop

Minor corrections for README.md -- fs.rename, "agruments" typo, fs.link ...

I'll also sync with the project page on js-platform.github.io/idbfs
refactoring to support additional backends
Merge pull request #32 from js-platform/backend-refactoring

refactoring to support additional backends
removed a bunch of promisey code; converted to callbacks
removed all uses of promises; remove promise library since it's not longer needed