Include libicu-dev in the build

[fresheneesz]

npm install should be enough to install node-stringprep. The user shouldn't have to do a bunch of other crap to get this to install - thats the whole point of a package management system like npm.

I think you can probably just put an appropriate preinstall script in package.json that checks what kind of linux you have and runs the right stuff to install libicu.

[mcfiredrill]

Or it could at least check the version of libicu and abort if its too old.

[mcfiredrill]

Although it looks like it should here:
https://github.com/node-xmpp/node-stringprep/blob/master/wscript#L16