Add User-Agent header in every request

[samwierema]

Preferably something like this:

<node.js or io.js>/<version>

Real example would look like:

node.js/0.10
io.js/1.3.0

[fvdm]

io.js v4.0 will be merged with node.js later this year, then they will continue as node v4.0

For now node is always 0.x and io.js is always >1.x so using only node.js/1.3.0 still covers both.

[samwierema]

Ok, great. So it will be: node.js/<version>.

[fvdm]

Alright, done.