Drafted some general API documentation
Merge pull request #28 from JuliaLang/in/api_doc

Drafted some general API documentation
tweaks to API docs as per discussion
Duck typing and consistent return types (Vector{typeof(y0)}) for all solvers. Changed order of arguments to F,y0,tspan. Added keyword jacobian for ode4s*. Tests adjusted accordingly.
Fixed deprecation warning for + in fdjacobian and ode4.
Merge pull request #14 from acroy/api-yout

RFC: Duck typing and consistent return types for all solvers.