Is this package version number following semver?

**Background**:

Recently I had to wipe out my old `package-lock.json` which kept me at `1.4.x` because I lost access to the private instance of NPM registry I used to have.
Current latest was installed: `1.8.2`

**Problem**:
It made my app throw errors saying some function from _aureliaPal.DOM is not there.

**Solution**:
Eventually I found out that there's `aurelia-pal` and `aurelia-pal-browser` now and one needs to call `initialize`. Everything is OK now.

But that made me think: the constraint was expressed `^1.4.0` so npm was allowed to install `1.8.2` once I removed the lock. The problem is that `1.5.0` is not backwards compatible with `1.4.0`. It's requird to initialize the PAL. Once I found that out I was like: "PAL is really a great idea!", but there's also no notice about that in the readme.

I imagine users of `aurelia-fetch-client` inside `aurelia-framework` have no such problem (I have no aurelia apps to find out quickly)

I suggest at least a notice about how to use the `aurelia-fetch-client` package stand-alone should be added to the readme. I'm using `aurelia-fetch-client` stand-alone, without `aurelia-framework`. I do it because I like its features but the app it's used in is not aurelia app. It would be great to have it mentioned in readme in here and in any other packages suitable to be used stand-alone as well.

Start with the README and review the existing standalone usage guidance for aurelia-fetch-client, including the need to call initialize after using aurelia-pal and aurelia-pal-browser. Done means the README clearly documents standalone use and the initialization requirement for users outside aurelia-framework.

Written by the indexing model from the issue text.