Use ECOS 1.0.3 + Add setup function that takes keyword arguments

I haven't really made pull requests in the past, so apologies if this isn't the right etiquette.

Two main changes:

1. Instead of using ecos-master, I'm using version 1.0.3 of ECOS so it doesn't break unexpectedly.
2. I have added another setup function that takes in keyword arguments. It allows sparse matrices for A and G to be specified, as well as allowing them to be `nothing` in case there are no conic inequalities etc.

In terms of testing, CVX.jl is currently using my fork of ECOS.jl and seems to be working fine: https://github.com/karanveerm/CVX.jl/blob/master/src/solvers/ecos.jl. Let me know if you'd like any changes/ have any problems. Thanks!