Build bundled racer

[vosen]

Currently, we are shipping racer binaries. Better solution would be to add racer submodule and .rsproj project that builds it.
I'm not sure how possible it's at the moment but with project pages not being yet implemented that will require manual work with .rsproj.
Also, this will probably require adding support for loading project from nested path (currently we only allow crate root module to be <location of project.rsproj>\src\main.rs or <location of project.rsproj>\src\lib.rs, but if we are to use submodules we will want support for <location of project.rsproj>\arbitrary\nested\path\to\src\main.rs)

[MaulingMonkey]

It might be preferable to switch to relying on a rustup provided racer at this point?