Support taking PUT payload from stdin

[davidebbo]

I've been thinking that scenarios would be easier in PowerShell is we take in the payload from stdin instead of (or as an alternative to?) using a switch. e.g., suppose you have the json payload in a $json variable.

You can't write: ARMTemplate PUT /path -content $json, because you're up against nearly unsolvable quoting issues. But you can write $json | ARMTemplate PUT /path as that avoids all the quoting issues. It's also simpler.

[suwatch]

Fix by 77975a1