Too much escaping in `@objective`

[rdeits]

@objective escapes its entire result, which assumes that setobjective! and @expression are defined in the caller's scope:

julia> module Foo
       using SimpleQP: @objective, Model, Minimize
       using OSQP.MathOptInterfaceOSQP: OSQPOptimizer
       m = Model(OSQPOptimizer())
       @objective(m, Minimize, 0)
       end
WARNING: replacing module Foo
ERROR: UndefVarError: @expression not defined