Proposal: make comptime chameleon immutable

Hi there, First of all thanks for this lib :D ! I would have a small improvement on the comptime api to propose. The proposed change is to make the comptime Chameleon an immutable struct, which mean at every style change a new struct is produced. This make the use of the lib in comptime environment easier (at least for me '^^) I have implemented it on a fork, you can find it here: https://github.com/Selveris/chameleon-fork If you find the change useful feel free to take it Edit: Also an added bonus (?) is that now every Chameleon struct is a Preset