Bring back old logo into svg

As a big fan of the old logo, if @thomassuckow is [right](https://github.com/flackr/circ/commit/ee19605abbcc74e9e1cb6526eddf7df2d456b6e1#commitcomment-6509762)  and the logo change just to get a logo in the svg format, here it is (it may not be perfect but seem okay).

If this is for an other reason, then forgot this PR :)