Emit hex version of codepoint

[backflip]

As discussed in backflip/gulp-iconfont-css#9

[nfroidure]

After some thinking, i think the best is to keep codepoints as integers, for compatibility reasons, but also cause it is the more memory efficient way to store the information.

Imha, a plugin responsibility is to provide information in an universal and lightweight format instead of assuming which usage users will make of its information. As pointed out by your PR, doing a codepoint.toString(16) is simple enough to let users manage this conversion.

I'll add it to the usage section of the REAME to help users but wont merge this PR. Sorry 'bout that, hope you'll agree on my thoughts.

[backflip]

Sounds absolutely reasonable.